Math CentralQuandaries & Queries


Question from Heather, a student:

Tom took a collection of tiles from a box. Sue took 13 and Bob took half of those remaining. Tom had 11 left. How many did they start with?

Hi Heather,

This is an example of what I call a "working backwards problem". If you go to the Quandaries and Queries page on Math Central and use the Quick Search to search for the term working backwards you will find many problems of this type.

For your question, when Tom got the tiles there were 11 left. Just before that Bob took half the tiles which left 11 for Tom. How many tiles were there when Bob got to take his? How many tiles were there when Sue got to take her 13?

Check your answer by working forward.


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