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Algebra Readiness Chapter 1 Section 3 Lesson 1.3 Use Formulas Vocabulary and Concepts: A variable is a letter used to represent one or more numbers. A formula gives a relationship between two or more variables. Some common formulas are as follows: Perimeter and Area of a Rectangle The perimeter p of a rectangle with length l and width w is : P=2l + 2w The area A of a rectangle with length l and width w is: A = lw Perimeter and Area of a Square The perimeter p of a square with side length s is: P =4s The area A of a square with side length s is: A = s² Distance, Rate, and Time Distance traveled d is equal to the speed (rate of travel) r times the travel time t. d=rt Total Cost The total cost T of n items is the cost c of one item (the unit cost) times the number of items. T=cn Example 1 Finding Perimeter and Area International soccer is played on a rectangular field that has a length of 100 meters and a width of 64 meters. What are the perimeter and the area of the soccer field? SOLUTION P = 2l + 2w = 2 (100) + 2(64) Write perimeter formula. Substitute 100 for l and 64 for w. = 200 + 128 Multiply. = 328 Add. You Try: A picture frame holds a picture that has a length of 6 inches and a width of 4 inches. What are the perimeter and the area of the picture? Answer: What is the length? 6 in. What is the width? 4 in. What is the formula for perimeter for this shape? P= 2l + 2w P = 2(6) + 2(4) = 12 + 8 = 20 in. What is the formula for area for this shape? A=lw A=6(4) = 24 in.² Example 2: Finding distance traveled. A sea turtle travels at an average rate of about 20 kilometers per day. How far can a sea turtle travel in 4 days? d = rt = 20 · 4 Write the formula for distance traveled. Substitute 20 for r and 4 for t. = 80 km Multiply. A sea turtle can travel 80 kilometers in 4 days. Example 3: Finding total cost. A school is purchasing 35 microscopes that cost $119 each for the science department. What is the total cost? T = cn = 119 · 35 = 4165 Write the formula for total cost. Substitute 119 for c and 35 for n. Multiply. The total cost for 35 microscopes that cost $119 each is $4165. You Try: Kayla bought 26 jars of poster paint. She paid $3 for each jar. What was the total cost? Answer: What is the formula for finding total cost? T = cn What is the cost of one item? $3 What is the number of items? 26 T = 3 · 26 = $78