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The Test of Reasonableness In general applying a test of reasonableness to an answer means looking at it in relation to the numbers operated upon to determine if it’s “in the ballpark.” Put in simple terms, you look at the answer to see if it makes sense. For example, if you determine 10% of $75 to $750, you should immediately notice something is very wrong, because 10% of something is much smaller than the original amount. The test of reasonableness comes very much into play in word problems. For example, questions asking for length, dollars, or time should never give negative answers because those things would not make sense if they were negative (what is -3 feet?). Also, think about what the answer should be. If I invest $400 dollars in a bank at 8% interest for 3 years, I would expect the balance to be larger than the original amount that I invested (that’s why we put money in the bank!), so an answer that is smaller than $400 is obviously wrong. Translating Verbal Expressions into Mathematical Expressions Verbal Expressions added to more than the sum of increased by the total of Examples 6 added to y 8 more than x the sum of x and z t increased by 9 the total of 5 and y Math Translation 6+y 8+x x+z t+9 5+y minus less than subtracted from decreased by the difference between x minus 2 7 less than t 5 subtracted from 8 m decreased by 3 the difference between y and 4 x-2 t-7 8-5 m-3 y-4 10 times 2 one half of 6 the product of 4 and 3 10 X 2 (1/2) X 6 4X3 multiplied by y multiplied by 11 11y Division divided by the quotient of the ratio of x divided by 12 the quotient of y and z the ratio of t to 9 x/12 y/z t/9 Power the square of the cube of squared the square of x the cube of z y squared x 3 z 2 y Equivalency equals is is the same as 1+2 equals 3 2 is half of 4 ½ is the same as 2/4 1+2 = 3 2 = (½)X4 yields represents 3+1 yields 4 y represents x+1 3+1 = 4 y=x+1 greater than less than greater than or equal to at least no less than less than or equal to at most no more than -3 is greater than -5 -3 > -5 -5 is less then -3 -5 < -3 x is greater than or equal to 5 x ≥ 5 Addition Subtraction Multiplication times of the product of 2 1 2 2 4 Comparison x is at least 80 x is no less than 70 x is less then or equal to -6 y is at most 23 y is no more than 21 x ≥ 80 x ≥ 70 x ≤ -6 y ≤ 23 y ≤ 21 Solving Application Problems Problem-Solving Strategy: 1) Analyze the problem. What are you trying to find? What’s the given info? 2) Work out a plan before starting. Draw a sketch if possible. Look for indicator words (e.g. gained, lost, times, per) to know which operations (+,-, x,÷) to use. 3) Estimate a reasonable answer. 4) Solve the problem. 5) Check your work. If the answer is not reasonable, start over. Example: Each home in a subdivision requires 180 ft of fencing. Find the number of homes that can be fenced with 5760 ft of fencing material. 1) What are we trying to find? Total number of homes that can be fenced. Given info: 5760 ft of material, 180 ft of fencing per home. 2) Work out a plan. We want to know how many homes can be fenced with 5760 ft of fencing. If we divide 180 feet per home into 5760 feet we will get the total number of homes ( The feet units cancel out). 3) Estimate a reasonable answer. Round 5760 to 6000 and 180 to 200. 6000÷200 = 30 4) Solve the problem. See below. 5) Check your work. Check division. Does 32x18=5760 ? Yes. Is 32 close to our estimate, 30? Yes. So our answer is 32 homes. (Make sure the units “homes” is in the answer!) 5760 ft 1 home 5760 32 homes 180 ft 180 32 180 5760 - 540 360 - 360 0