The chess club is planning a trip to LaGrange, which is a 6

hour drive. They plan to make one lunch stop of 45 minutes and two

other 15-minute stops. They want to arrive at 4:30 P.M. What time

should they leave?

Try, Check, and Revise and Work BackwardTry, Check, and Revise and Work BackwardCOURSE 3 LESSON 4-7COURSE 3 LESSON 4-7

The goal is to find what time they should leave. The driving time is 6 hours. They want to make a 45-minute lunch stop plus two other 15-minute stops and arrive at 4:30 P.M.

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Try, Check, and Revise and Work BackwardTry, Check, and Revise and Work BackwardCOURSE 3 LESSON 4-7COURSE 3 LESSON 4-7

Method 1 Try, Check, and Revise

The drive time is 6 hours. The 45-minute lunch stop plus two other 15-minute stops adds 1 hour and 15 minutes. The total trip time is 7 hours and 15 minutes. Make a reasonable guess. If the guess does not solve the problem, use the result to determine a better value to test.

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Try, Check, and Revise and Work BackwardTry, Check, and Revise and Work BackwardCOURSE 3 LESSON 4-7COURSE 3 LESSON 4-7

Test Value Total Trip Time Arrival Time Conclusion

8 A.M. 7 hours and 3:15 P.M. Too early15 minutes

10:30 A.M. 7 hours and 5:45 P.M. Too late15 minutes

9:15 A.M. 7 hours and 4:30 P.M. Correct15 minutes

They should leave at 9:15 A.M.

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Try, Check, and Revise and Work BackwardTry, Check, and Revise and Work BackwardCOURSE 3 LESSON 4-7COURSE 3 LESSON 4-7

Method 2 Work Backward

Since this problem gives a final time and asks for an initial time, work backward is a good strategy to use.

• The final time is 4:30 P.M. The actual time driving is 6 hours. Counting back 6 hours from 4:30 brings you to 10:30 A.M.

• Lunch takes 45 minutes. Counting back 45 minutes from 10:30 A.M. brings you to 9:45 A.M.

• Two other 15-minute stops take up 30 minutes. Counting back 30 minutes from 9:45 A.M. brings you to 9:15 A.M. So the chess team would have to leave at 9:15 A.M. to arrive at 4:30 P.M.

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Try, Check, and Revise and Work BackwardTry, Check, and Revise and Work BackwardCOURSE 3 LESSON 4-7COURSE 3 LESSON 4-7

Since both methods result in the same starting time, the answer checks. You can also check by starting with 9:15 A.M.

Start

9:15 A.M.

Driving Time

9:15 A.M. plus 6 hours= 3:15 P.M.

Lunch and Two Stops

3:15 plus 1 hour and 15 minutes= 4:30 P.M.

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Try, Check, and Revise and Work BackwardTry, Check, and Revise and Work Backward

Solve by either try, test, and revise or work backward.

Rita deposited $500 into her account last Friday, withdrew $150 on Tuesday, and withdrew $200 more on Wednesday. After depositing $50, she withdrew half her money. She had $3,100 remaining. What amount did she have before her deposit last Friday?

$6,000

COURSE 3 LESSON 4-7COURSE 3 LESSON 4-7

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