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Chabot Mathematics §3.2a System Applications Bruce Mayer, PE Licensed Electrical & Mechanical Engineer [email protected] Chabot College Mathematics 1 Bruce Mayer, PE [email protected] • MTH55_Lec-10_sec_3-1_2Var_LinSys_ppt Review § 3.1 MTH 55 Any QUESTIONS About • §’s3.1 → Systems of Linear Equations Any QUESTIONS About HomeWork • §’s3.1 → HW-08 Chabot College Mathematics 2 Bruce Mayer, PE [email protected] • MTH55_Lec-10_sec_3-1_2Var_LinSys_ppt System Methods Compared We now have three distinctly different ways to solve a system. Each method has strengths & weaknesses Method Strengths Weaknesses Graphical Solutions are displayed visually. Works with any system that can be graphed. Inexact when solutions involve numbers that are not integers or are very large and off the graph. Substitution Always yields exact solutions. Easy to use when a variable is alone on one side of an equation. Introduces extensive computations with fractions when solving more complicated systems. Solutions are not graphically displayed. Elimination Always yields exact solutions. Solutions are not graphically Easy to use when fractions or displayed. decimals appear in the system. Chabot College Mathematics 3 Bruce Mayer, PE [email protected] • MTH55_Lec-10_sec_3-1_2Var_LinSys_ppt Solving Application Problems 1. Read the problem as many times as needed to understand it thoroughly. Pay close attention to the questions asked to help identify the quantity the variable(s) should represent. In other Words, FAMILIARIZE yourself with the intent of the problem • Often times performing a GUESS & CHECK operation facilitates this Familiarization step Chabot College Mathematics 4 Bruce Mayer, PE [email protected] • MTH55_Lec-10_sec_3-1_2Var_LinSys_ppt Solving Application Problems 2. Assign a variable or variables to represent the quantity you are looking for, and, when necessary, express all other unknown quantities in terms of this variable. That is, Use at LET statement to clearly state the MEANING of all variables • Frequently, it is helpful to draw a diagram to illustrate the problem or to set up a table to organize the information Chabot College Mathematics 5 Bruce Mayer, PE [email protected] • MTH55_Lec-10_sec_3-1_2Var_LinSys_ppt Solving Application Problems 3. Write an equation or equations that describe(s) the situation. That is, TRANSLATE the words into mathematical Equations 4. Solve the equation(s); i.e., CARRY OUT the mathematical operations to solve for the assigned Variables 5. CHECK the answer against the description of the original problem (not just the equation solved in step 4) Chabot College Mathematics 6 Bruce Mayer, PE [email protected] • MTH55_Lec-10_sec_3-1_2Var_LinSys_ppt Solving Application Problems 6. Answer the question asked in the problem. That is, make at STATEMENT in words that clearly addressed the original question posed in the problem description Chabot College Mathematics 7 Bruce Mayer, PE [email protected] • MTH55_Lec-10_sec_3-1_2Var_LinSys_ppt Example Problem Solving Two angles are supplementary. One of the angles is 20° larger than three times the other. Find the two angles 1. Familarize • Recall that two angles are supplementary if the sum of their measures is 180°. We could try and guess, but instead let’s make a drawing and translate. Let x and y represent the measures of the two angles Chabot College Mathematics 8 Bruce Mayer, PE [email protected] • MTH55_Lec-10_sec_3-1_2Var_LinSys_ppt Example Problem Solving 1. Familarize with Diagram x y 2. Translate Since the angles are supplementary, one equation is x + y = 180 (1) The second sentence can be rephrased and translated as follows: Chabot College Mathematics 9 Bruce Mayer, PE [email protected] • MTH55_Lec-10_sec_3-1_2Var_LinSys_ppt Example Problem Solving 2. Translating Rewording and Translating One angle is 20 more than three times the other y • We now have a system of two equations and two unknowns. Chabot College Mathematics 10 = 20 + 3x (2) x y 180 1 2 y 20 3x Bruce Mayer, PE [email protected] • MTH55_Lec-10_sec_3-1_2Var_LinSys_ppt Example Problem Solving 3. Carry Out x y 180 1 2 y 20 3x x 20 3x 180 4x 20 180 4 x 160 x 40 • Sub x = 40° in Eqn-1 x y 180 40 y 180 y 140 Chabot College Mathematics 11 Bruce Mayer, PE [email protected] • MTH55_Lec-10_sec_3-1_2Var_LinSys_ppt Example Problem Solving 4. Check • If one angle is 40° and the other is 140°, then the sum of the measures is 180°. Thus the angles are supplementary. If 20° is added to three times the smaller angle, we have 3(40°) + 20° = 140°, which is the measure of the other angle. The numbers check. 5. STATE • One angle measures 40° and the other measures 140° Chabot College Mathematics 12 Bruce Mayer, PE [email protected] • MTH55_Lec-10_sec_3-1_2Var_LinSys_ppt Elimination Applications Total-Value Problems Mixture Problems Chabot College Mathematics 13 Bruce Mayer, PE [email protected] • MTH55_Lec-10_sec_3-1_2Var_LinSys_ppt Total Value Problems EXAMPLE: Lupe sells concessions at a local sporting event. • In one hour, she sells 72 drinks. The drink sizes are – small, which sells for $2 each – large, which sells for $3 each. • If her total sales revenue was $190, how many of each size did she sell? Chabot College Mathematics 14 Bruce Mayer, PE [email protected] • MTH55_Lec-10_sec_3-1_2Var_LinSys_ppt Example Drinks Sold 1. Familiarize. • Suppose (i.e., GUESS) that of the 72 drinks, 20 where small and 52 were large. • The 72 drinks would then amount to a total of 20($2) + 52($3) = $196. Although our guess is incorrect (but close), checking the guess has familiarized us with the problem. Chabot College Mathematics 15 Bruce Mayer, PE [email protected] • MTH55_Lec-10_sec_3-1_2Var_LinSys_ppt Example Drinks Sold 1. Familiarize – LET: • s = the number of small drinks and • l = the number of large drinks 2. Translate. • Since a total of 72 drinks were sold, we must have s + l = 72. • To find a second equation, we reword some information and focus on the income from the drinks sold Chabot College Mathematics 16 Bruce Mayer, PE [email protected] • MTH55_Lec-10_sec_3-1_2Var_LinSys_ppt Example Drinks Sold 2. Translate. • $3 Translating & Rewording Income from Income from small drinks Plus large drinks $2s Thus we have Constructed the System Chabot College Mathematics 17 + $2 Totals $190 = $190 $3l s l 72 2s 3l 190 1 2 Bruce Mayer, PE [email protected] • MTH55_Lec-10_sec_3-1_2Var_LinSys_ppt Example Drinks Sold 3. Carry Out s l 72 1 l 72 s 3 2s 3l 190 Solve (1) for l 2s 372 s 190 Use (3) to Sub for l in (2) 2s 216 3s 190 Use Distributive Law 216 190 3s 2s Combine Terms s 26 Simplify to find s Sub s = 26 in (3) to Find l l 72 26 Chabot College Mathematics 18 l 46 Bruce Mayer, PE [email protected] • MTH55_Lec-10_sec_3-1_2Var_LinSys_ppt 2 Example Drinks Sold 4. Check: If Lupe sold 26 small and 46 large drinks, she would have sold 72 drinks, for a total of: 26($2) + 46($3) = $52 + $138 = $190 5. State: Lupe sold • 26 small drinks • 46 large drinks Chabot College Mathematics 19 Bruce Mayer, PE [email protected] • MTH55_Lec-10_sec_3-1_2Var_LinSys_ppt Problem-Solving TIP When solving a problem, see if it is patterned or modeled after a problem that you have already solved. Chabot College Mathematics 20 Bruce Mayer, PE [email protected] • MTH55_Lec-10_sec_3-1_2Var_LinSys_ppt Example Problem Solving A cookware consultant sells two sizes of pizza stones. The circular stone sells for $26 and the rectangular one sells for $34. In one month she sold 37 stones. If she made a total of $1138 from the sale of the pizza stones, how many of each size did she sell? Pizza Stone Chabot College Mathematics 21 Bruce Mayer, PE [email protected] • MTH55_Lec-10_sec_3-1_2Var_LinSys_ppt Example Pizza Stones 1. Familiarize – When faced with a new problem, it is often useful to compare it to a similar problem that you have already solved. Here instead of $2 and $3 drinks, we are counting $26 & $34 pizza stones. So LET: • c = the no. of circular stones • r = the no. of rectangular stones Chabot College Mathematics 22 Bruce Mayer, PE [email protected] • MTH55_Lec-10_sec_3-1_2Var_LinSys_ppt Example Pizza Stones cont.2 2. Translate – Since a total of 37 stones were sold, we have: c + r = 37 • Tabulating the Data Can be Useful Circular Rectangular Cost per pan $26 $34 Number of pans c r 26c 34r Money Paid Chabot College Mathematics 23 Total 37 $1138 c + r = 37 26c + 34r = 1138 Bruce Mayer, PE [email protected] • MTH55_Lec-10_sec_3-1_2Var_LinSys_ppt Example Pizza Stones 2. Translate – We have translated to a system of equations: c + r = 37 (1) 26c + 34r = 1138 (2) 3. Carry Out Multiply Eqn(1) by −26 26c 26r 962 Add Eqns (2)&(3): Chabot College Mathematics 24 3 26c 34r 1138 26c 26r 962 0c 8r 176 Bruce Mayer, PE [email protected] • MTH55_Lec-10_sec_3-1_2Var_LinSys_ppt 2 3 Example Pizza Stones cont.4 3. Carry Out – Solve for r 8r 176 r 176 8 r 22 • Find c using Eqn (1): c r 37 c 22 37 c 37 22 15 4. Check: If r = 22 and c = 15, a total of 37 stones were sold. The amount paid was 22($34) + 15($26) = $1138 5. State: The consultant sold 15 Circular and 22 rectangular pizza stones Chabot College Mathematics 25 Bruce Mayer, PE [email protected] • MTH55_Lec-10_sec_3-1_2Var_LinSys_ppt Example Mixture Problem A Chemical Engineer wishes to mix a reagent that is 30% acid and another reagent that is 50% acid. How many liters of each should be mixed to get 20 L of a solution that is 35% acid? Chabot College Mathematics 26 Bruce Mayer, PE [email protected] • MTH55_Lec-10_sec_3-1_2Var_LinSys_ppt Example Acid Mixxing 1. Familiarize. Make a drawing and then make a guess to gain familiarity with the problem • The Diagram t liters + 30% acid Chabot College Mathematics 27 f liters = 50% acid 20 liters 35% acid Bruce Mayer, PE [email protected] • MTH55_Lec-10_sec_3-1_2Var_LinSys_ppt Example Acid Mixxing To familiarize ourselves with this problem, guess that 10 liters of each are mixed. The resulting mixture will be the right size but we need to check the Pure-Acid Content: 0.30(10) 0.50(10) 8 L. Our 10L guess produced 8L of pure-acid in the mix, but we need 0.35(20) = 7L of pure-acid in the mix Chabot College Mathematics 28 Bruce Mayer, PE [email protected] • MTH55_Lec-10_sec_3-1_2Var_LinSys_ppt Example Acid Mixxing 2. Translate: LET • t = the number of liters of the 30% soln • f = the number of liters of the 50% soln Next Tabulate the calculation of the amount of pure-acid in each of the mixture components Chabot College Mathematics 29 Bruce Mayer, PE [email protected] • MTH55_Lec-10_sec_3-1_2Var_LinSys_ppt Example Acid Mixxing Pure-Acid Calculation Table First Solution Second Solution Mixture Number of Liters t f 20 Percentage of Acid 30% 50% 35% Amount of Acid 0.30t 0.50f 7 t + f = 20 0.30t + 0.50f = 7 The Table t f 20, Reveals a System 0.30t 0.50 f 7. of Equations Chabot College Mathematics 30 Bruce Mayer, PE [email protected] • MTH55_Lec-10_sec_3-1_2Var_LinSys_ppt Example Acid Mixxing 3. Carry Out: Solve Eqn System t f 0.30t 0.50 f 20 7 1 2 Eliminate f by multiplying both sides –0.50t – 0.50f = –10 of equation (1) by −0.5 0.30t + 0.50f = 7 and adding them to the –0.20t = –3 corresponding sides of t = 15. equation (2): Chabot College Mathematics 31 Bruce Mayer, PE [email protected] • MTH55_Lec-10_sec_3-1_2Var_LinSys_ppt Example Acid Mixxing To find f, we substitute 15 for t in equation (1) and then solve for f: 15 + f = 20 f=5 Obtain soln (15, 5), or t = 15 and f = 5 4. Check: Recall t is the of liters of 30% soln and f is the of liters of 50% soln Number of liters: t + f = 15 + 5 = 20 Amount of Acid: 0.30t + 0.50f = 0.30(15) + 0.50(5) = 7 Chabot College Mathematics 32 Bruce Mayer, PE [email protected] • MTH55_Lec-10_sec_3-1_2Var_LinSys_ppt Example Wage Rate Ethan and Ian are twins. They have decided to save all of the money they earn at their part-time jobs to buy a car to share at college. One week, Ethan worked 8 hours and Ian worked 14 hours. Together they saved $256. The next week, Ethan worked 12 hours and Ian worked 16 hours and they earned $324. How much does each twin make per hour? • i.e.; What are the Wage RATES Chabot College Mathematics 33 Bruce Mayer, PE [email protected] • MTH55_Lec-10_sec_3-1_2Var_LinSys_ppt Example Wage Rate In This Case LET: • E ≡ Ethan’s Wage Rate ($/hr) • I ≡ Ian’s Wage Rate ($/hr) Translate: Ethan worked 8 hours and Ian worked 14 hours. Together they saved $256 8∙{Ethan’s Rt} plus 14∙{Ian’s Rt} is $256 8E 14I 256 Chabot College Mathematics 34 Bruce Mayer, PE [email protected] • MTH55_Lec-10_sec_3-1_2Var_LinSys_ppt Example Wage Rate Translate: Ethan worked 12 hours and Ian worked 16 hours and they earned $324. 12∙{Ethan’s Rt} plus 16∙{Ian’s Rt} is $324 12E 16I 324 Now have 2-Eqn System Chabot College Mathematics 35 14 I 256 12 E 16 I 324 8E Bruce Mayer, PE [email protected] • MTH55_Lec-10_sec_3-1_2Var_LinSys_ppt Example Wage Rate Carry Out 8E 12 E 96 E 14 I 25612 324 8 16 I 168I 96 E 128I 40 I Chabot College Mathematics 36 3072 2592 480 Bruce Mayer, PE [email protected] • MTH55_Lec-10_sec_3-1_2Var_LinSys_ppt Example Wage Rate 480 Carry Out 40 I 480 I 12 40 Sub I = 12 into 1st eqn to Find E 8E 1412 256 8E 256 168 8E 88 E 88 8 E 11 State Answer • Ethan Earns $11 per hour • Ian Earns $12 per hour Chabot College Mathematics 37 Bruce Mayer, PE [email protected] • MTH55_Lec-10_sec_3-1_2Var_LinSys_ppt Example Geometry The perimeter of a fence around the children’s section of the community park is 268 feet. The length is 34 feet longer than the width. Find the dimensions of the park. 1. Familiarize: Draw a Diagram and LET: • l ≡ the length • w ≡ the width Chabot College Mathematics 38 l w Bruce Mayer, PE [email protected] • MTH55_Lec-10_sec_3-1_2Var_LinSys_ppt Example Geometry 2. Translate. The Perimeter is 2l + 2w. The perimeter is 268 feet. 2l + 2w = 268 The length is 34 ft more than the width l Chabot College Mathematics 39 = 34 + w Bruce Mayer, PE [email protected] • MTH55_Lec-10_sec_3-1_2Var_LinSys_ppt Example Geometry Now have a system of two equations and two unknowns. • 2l + 2w = 268 (1) 2l 2w 268 • l = 34 + w (2) l 34 w 3. Solve for w using Substitution Method Chabot College Mathematics 40 2(34 w) 2w 268 68 2w 2w 268 68 4w 268 4w 200 w 50 Bruce Mayer, PE [email protected] • MTH55_Lec-10_sec_3-1_2Var_LinSys_ppt Example Geometry Sub 50 for w in one of the Orignal Eqns l = 34 + w = 34 + 50 = 84 feet 4. Check: If the length is 84 and the width is 50, then the length is 34 feet more than the width, and the perimeter is: 2(84) + 2(50), or 268 feet 5. State: The width is 50 feet and the length is 84 feet Chabot College Mathematics 41 Bruce Mayer, PE [email protected] • MTH55_Lec-10_sec_3-1_2Var_LinSys_ppt Example Mixture Problem A coffee shop is considering a new mixture of coffee beans. It will be created with Italian Roast beans costing $9.95 per pound and the Venezuelan Blend beans costing $11.25 per pound. The types will be mixed to form a 60-lb batch that sells for $10.50 per pound. How many pounds of each type of bean should go into the blend? Chabot College Mathematics 42 Bruce Mayer, PE [email protected] • MTH55_Lec-10_sec_3-1_2Var_LinSys_ppt Example Coffee Beans 1. Familiarize – This problem is similar to one of the previous examples. • • • Instead of pizza stones we have coffee beans We have two different prices per pound. Instead of knowing the total amount paid, we know the weight and price per pound of the new blend being made. LET: • • i ≡ no. lbs of Italian roast and v ≡ no. lbs of Venezuelan blend Chabot College Mathematics 43 Bruce Mayer, PE [email protected] • MTH55_Lec-10_sec_3-1_2Var_LinSys_ppt Example Coffee Beans 2. Translate – Since a 60-lb batch is being made, we have i + v = 60. • Present the information in a table. Italian Number of pounds v 60 Price per pound $9.95 $11.25 Value of beans 9.95i Chabot College Mathematics 44 i Venezuelan New Blend 11.25v i + v = 60 $10.50 630 9.95i + 11.25v = 630 Bruce Mayer, PE [email protected] • MTH55_Lec-10_sec_3-1_2Var_LinSys_ppt Example Coffee Beans cont.4 2. Translate - We have translated 1 i v 60 to a system of equations 9.95i 11.25v 630 2 3. Carry Out - When equation (1) is solved for v, we have: v = 60 − i. • We then substitute for v in equation (2). 9.95i 11.2560 i 630 9.95i 675 11.25i 630 1.30i 45 i 45 1.3 i 34.61 Chabot College Mathematics 45 Bruce Mayer, PE [email protected] • MTH55_Lec-10_sec_3-1_2Var_LinSys_ppt Example Coffee Beans cont.5 3. Carry Out - Find v using v = 60 − i. v 60 i 60 34.61 v 25.39 4. Check - If 34.6 lb of Italian Roast and 25.4 lb of Venezuelan Blend are mixed, a 60-lb blend will result. • The value of 34.6 lb of Italian beans is 34.6•($9.95), or $344.27. • The value of 25.4 lb of Venezuelan Blend is 25.4•($11.25), or $285.75, Chabot College Mathematics 46 Bruce Mayer, PE [email protected] • MTH55_Lec-10_sec_3-1_2Var_LinSys_ppt Example Coffee Beans cont.6 4. Check – cont. • so the value of the blend is [$344.27 + $285.75] = $630.02. • A 60-lb blend priced at $10.50 a pound is also worth $630, so our answer checks 5. State – The blend should be made from • • 34.6 pounds of Italian Roast beans 25.4 pounds of Venezuelan Blend beans Chabot College Mathematics 47 Bruce Mayer, PE [email protected] • MTH55_Lec-10_sec_3-1_2Var_LinSys_ppt Simple Interest If a principal of P dollars is borrowed for a period of t years with interest rate r (expressed as a decimal) computed yearly, then the total interest paid at the end of t years is I P r t Interest computed with this formula is called simple interest. When interest is computed yearly, the rate r is called an annual interest rate Chabot College Mathematics 48 Bruce Mayer, PE [email protected] • MTH55_Lec-10_sec_3-1_2Var_LinSys_ppt Example Simple Interest Ms. Jeung invests a total of $10,000 in Bonds from blue-chip and technology Companies. At the end of a year, the blue-chips returned 12% and the technology stocks returned 8% on the original investments. How much was invested in each type of Bond if the total interest earned was $1060? Chabot College Mathematics 49 Bruce Mayer, PE [email protected] • MTH55_Lec-10_sec_3-1_2Var_LinSys_ppt Example Simple Interest Familiarize: We are asked to find two amounts: • that invested in blue-chip Bonds • that invested in technology Bonds. If we know how much was invested in blue-chip Bonds, then we know that the rest of the $10,000 was invested in technology Bonds. Chabot College Mathematics 50 Bruce Mayer, PE [email protected] • MTH55_Lec-10_sec_3-1_2Var_LinSys_ppt Example Simple Interest TRANSLATE: LET • x ≡ amount invested in blue-chip bonds. • y ≡ amount invested in tech bonds Tabulate Interest Income Invest P t I = Prt Blue x 0.12 1 0.12x Tech y 0.08 1 0.08y Chabot College Mathematics 51 r Bruce Mayer, PE [email protected] • MTH55_Lec-10_sec_3-1_2Var_LinSys_ppt Example Simple Interest Translate TOTAL INTEREST statement Interest from Interest from Total + technology = Blue-chip Interest 0.12 x 0.08 y $1060 Translate TOTAL Principal statement {BluChip Prin.} plus {Tech Prin.} is $10k x y $10000 Chabot College Mathematics 52 Bruce Mayer, PE [email protected] • MTH55_Lec-10_sec_3-1_2Var_LinSys_ppt Example Simple Interest Carry Out: Solve Principal Eqn for y and then sub into Interest Eqn y 10,000 x & 0.12 x 0.08 y 1060 0.12x 0.08 10, 000 x 1060 0.12x 0.08 y 1060100 Clear Decimals 12x 8 10, 000 x 106, 000 12x 80, 000 8x 106, 000 4x 26, 000 Chabot College Mathematics 53 x 6500 Bruce Mayer, PE [email protected] • MTH55_Lec-10_sec_3-1_2Var_LinSys_ppt Example Simple Interest Back Substitute x 6500 & y 10,000 x x = 6500 into y 10000 6500 3500 Principal Eqn y 3500 to find y Check $3500 $6500 $10,000 12% of $6500 $780 8% of $3500 $280 Total interest earned = $1060. Chabot College Mathematics 54 Bruce Mayer, PE [email protected] • MTH55_Lec-10_sec_3-1_2Var_LinSys_ppt Example Simple Interest State: Ms. Jeung invested $3500 in technology Bonds and $6500 in blue-chip Bonds. Chabot College Mathematics 55 Bruce Mayer, PE [email protected] • MTH55_Lec-10_sec_3-1_2Var_LinSys_ppt WhiteBoard Work Problems From §3.2 Exercise Set • 22 Peppermint Patty Puzzled Chabot College Mathematics 56 Bruce Mayer, PE [email protected] • MTH55_Lec-10_sec_3-1_2Var_LinSys_ppt All Done for Today Commercial Coffee Bean Blending Chabot College Mathematics 57 Bruce Mayer, PE [email protected] • MTH55_Lec-10_sec_3-1_2Var_LinSys_ppt Chabot Mathematics Appendix r s r s r s 2 2 Bruce Mayer, PE Licensed Electrical & Mechanical Engineer [email protected] – Chabot College Mathematics 58 Bruce Mayer, PE [email protected] • MTH55_Lec-10_sec_3-1_2Var_LinSys_ppt