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. 


