Working Backwards
Lesson
Topic Index | Grade 4 Math | Elementary Test Prep | StudyZone

By applying the working backwards strategy, students find the solution to a problem by starting with the answer and using inverse operations to undo the steps stated in the problem.
e.g., a + b = c : c - a = b
 

A problem may tell you what happened at the end of a series of steps and ask you to find what happened at the beginning. To solve the problem, work backward step by step to the beginning.

Example

Brady was trying to decide when to get up in the morning. He needs 45 minutes to get ready for school. It takes him 25 minutes to drive to school. He wanted to get to school 20 minutes early to use the library. If school starts at 7:30, what time should he get up?
The problem gives you the amounts of time it will take to complete three tasks (45 minutes, 25 minutes, 20 minutes). It also tells you the time the last task must end (7:30). To solve the problem, work backward to the beginning.
Task Amount of Time Conclusion
1 Brady went to the library for 20 minutes. Then it was 7:30. He went to the library 20 minutes before 7:30, at 7:10.
2 He drove for 25 minutes. Then it was 7:10. He got in his car 25 minutes before 7:10, at 6:45.
3 He needed 45 minutes to get ready for school. Then it was 6:45. He began getting ready 45 minutes before 6:45, at 6:00.
Brady should get up by 6:00.

 

Remember:
The answer is found by starting with the end result and working back to the beginning.
 

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Topic Index | Grade 4 Math | Elementary Test Prep | StudyZone

Created by Carol A. Carroll
Updated by Nicole Freebern
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