course 2 lesson 4-7 4-7 kayla is bringing brownies to the sports banquet. she needs to be there by...
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COURSE 2 LESSON 4-7COURSE 2 LESSON 4-7
4-7
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?
141
4121
2
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.
141
4121
2
Try, Check, and Revise and Work Backward
COURSE 2 LESSON 4-7COURSE 2 LESSON 4-7
4-7
(continued)
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.
MakeBrownies
BakeBrownies
CoolBrownies
LeaveHome
Arrive atBanquet
Result
5:30 P.M. 5:45 P.M. 6:15 P.M. 7:45 P.M. 8:00 P.M. 45 min late
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.
Try, Check, and Revise and Work Backward
COURSE 2 LESSON 4-7COURSE 2 LESSON 4-7
4-7
(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.
Working backward shows that by starting the brownies at 4:45 P.M. Kayla will get to the banquet at 7:15 P.M.
Try, Check, and Revise and Work Backward
COURSE 2 LESSON 4-7COURSE 2 LESSON 4-7
4-7
(continued)
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.
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.
14
121
214
14
+ + 1 + = 2 h12
12
14
12
12
Try, Check, and Revise and Work Backward
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?
COURSE 2 LESSON 4-7COURSE 2 LESSON 4-7
4-7
34
6:00 A.M.
12
Try, Check, and Revise and Work Backward