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Try, Check, and Revise and Work Backward

Your goal is to find out the latest time Kayla can start making brownies and then arrive at the banquet at 7:15. It takes h to walk to the banquet, h to make the brownies, h to bake them, and 1 h for them to cool. 1 4. 1 4. 1 2. 1 2. COURSE 2 LESSON 4-7.

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Try, Check, and Revise and Work Backward

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  1. Your goal is to find out the latest time Kayla can start making brownies and then arrive at the banquet at 7:15. It takes h to walk to the banquet, h to make the brownies, h to bake them, and 1 h for them to cool. 1 4 1 4 1 2 1 2 COURSE 2 LESSON 4-7 Try, Check, and Revise and Work Backward Kayla is bringing brownies to the sports banquet. She needs to be there by 7:15 P.M. It will take Kayla’s family h to walk from their apartment to school. The brownies take hour to make, hour to bake, and 1 hours to cool. What is the latest time Kayla can start making the brownies so they will be cool before she leaves for the banquet? 1 4 1 4 1 2 1 2 4-7

  2. Method 1 Try, Check, and Revise Choose a value that makes sense and then check it. If your first check is not a solution, use the result to revise your estimate. Make Brownies Bake Brownies Cool Brownies Leave Home Arrive at Banquet Result 5:30 P.M. 5:45 P.M. 6:15 P.M. 7:45 P.M. 8:00 P.M. 45 min late COURSE 2 LESSON 4-7 Try, Check, and Revise and Work Backward (continued) Starting the brownies at 5:30 P.M. causes Kayla to arrive 45 min later than intended. Therefore, by starting the brownies 45 min earlier, at 4:45 P.M. , Kayla will arrive at 7:15 P.M. 4-7

  3. Working backward shows that by starting the brownies at 4:45 P.M. Kayla will get to the banquet at 7:15 P.M. COURSE 2 LESSON 4-7 Try, Check, and Revise and Work Backward (continued) Method 2  Work Backward You know that the series of events must end at 7:15 P.M. It makes sense to work backward to find when Kayla must start making the brownies. 4-7

  4. 1 2 1 4 1 2 It takes h to make the brownies, h to bake, and 1 h to cool. It takes h to walk to the banquet. Add these times to find the total time from when Kayla starts the brownies to when she arrives at the banquet. 1 4 1 2 1 4 1 2 1 2 1 4 1 2 + + 1 + = 2 h Subtract 2 h from 7:15 P.M. and you find that Kayla must start making the brownies at 4:45 P.M. The answer checks. COURSE 2 LESSON 4-7 Try, Check, and Revise and Work Backward (continued) 4-7

  5. COURSE 2 LESSON 4-7 Try, Check, and Revise and Work Backward 1 2 You need to be in school at 7:45 A.M. It takes you h to shower and brush your teeth, 10 min to get dressed, and 20 min to eat breakfast. The bus, which picks you up outside your house, takes h to get to school. What is the latest time you should get up in the morning? 3 4 6:00 A.M. 4-7

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