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§ 2.5 An Introduction to Problem Solving

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Martin-Gay, Beginning Algebra, 5ed 22 Strategy for Problem Solving General Strategy for Problem Solving 1)UNDERSTAND the problem Read and reread the problem Choose a variable to represent the unknown Construct a drawing, whenever possible Propose a solution and check 2)TRANSLATE the problem into an equation 3)SOLVE the equation 4)INTERPRET the result Check the proposed solution in the problem State your conclusion

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Martin-Gay, Beginning Algebra, 5ed 33 The product of twice a number and three is the same as the sum of five times the number and 12. Find the number. 1.) UNDERSTAND Read and reread the problem. If we let x = the unknown number, then “twice a number” translates to 2x, “the product of twice a number and three” translates to 2x · 3, “five times the number” translates to 5x, and “the sum of five times the number and 12” translates to 5x Finding an Unknown Number Example: Continued

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Martin-Gay, Beginning Algebra, 5ed 44 The product of · twice a number 2x2x and 3 3 is the same as = 5 times the number 5x5x and the sum of + Finding an Unknown Number Example continued: 2.) TRANSLATE Continued

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Martin-Gay, Beginning Algebra, 5ed 55 Finding an Unknown Number Example continued: 3.) SOLVE 2x · 3 = 5x x = 5x + 12 Simplify left side. x = 12 Simplify both sides. 6x + (– 5x) = 5x + (– 5x) + 12 Add –5x to both sides. 4.) INTERPRET Check: Replace “number” in the original statement of the problem with 12. The product of twice 12 and 3 is 2(12)(3) = 72. The sum of five times 12 and 12 is 5(12) + 12 = 72. We get the same results for both portions. State: The number is 12.

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Martin-Gay, Beginning Algebra, 5ed 66 A car rental agency advertised renting a Buick Century for $24.95 per day and $0.29 per mile. If you rent this car for 2 days, how many whole miles can you drive on a $100 budget? 1.) UNDERSTAND Read and reread the problem. Let’s propose that we drive a total of 100 miles over the 2 days. Then we need to take twice the daily rate and add the fee for mileage to get 2(24.95) (100) = = This gives us an idea of how the cost is calculated, and also know that the number of miles will be greater than 100. If we let x = the number of whole miles driven, then 0.29x = the cost for mileage driven Solving a Problem Example: Continued

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Martin-Gay, Beginning Algebra, 5ed 77 Solving a Problem Example continued: 2.) TRANSLATE Continued Daily costs 2(24.95) mileage costs 0.29x plus + is equal to = 100 maximum budget

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Martin-Gay, Beginning Algebra, 5ed 88 Solving a Problem Example continued: 3.) SOLVE Continued 2(24.95) x = x = 100 Simplify left side. 0.29x = Simplify both sides. Divide both sides by x Simplify both sides. Subtract from both sides – x = 100 – 49.90

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Martin-Gay, Beginning Algebra, 5ed 99 Solving a Problem Example continued: 4.) INTERPRET Check: Recall that the original statement of the problem asked for a “whole number” of miles. If we replace “number of miles” in the problem with 173, then (173) = , which is over our budget. However, (172) = 99.78, which is within the budget. State: The maximum number of whole number miles is 172.

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