Math CentralQuandaries & Queries


Question from Kim:

I cannot remember my combo to this simple lockbox. It is 3 digits- from 0-9. They can be used more than once . I thought it was 117..but no joy. I am fairly sure it was using those digits 1, and 7. can you give me a list of all possible combinations, using 1s and 7s, for the 3 number code? Thank you and I am in awe of people who have math skills, for I certainly do not.

Hi Kim,

Think of the possible combinations in an orderly fashion.

Suppose there are three ones then there is only one possibility,


Suppose there are two ones then you could have

117, 171, or 711.

What are the possible combinations with one one? What about no ones?

In total there are 8 possible combinations. Did any of them work?


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