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, 2013

Number theory Difficulty 1.1 Junior Find the answer Canada

Which of the following numbers is a multiple of 9?

Pick one

Solution

Solution 1

A number is a multiple of 9 if it is the result of multiplying 9 by an integer.
Of the answers given, only 45 results from multiplying 9 by an integer, since $45=9\times5$ .

Solution 2

A number is a multiple of 9 if the result after dividing it by 9 is an integer.
Of the answers given, only 45 results in an integer after dividing by 9, since $45\div9=5$ .

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Source: CEMC, University of Waterloo, licensed CC-BY-NC-4.0. Statement reproduced verbatim; metadata (topic, difficulty) added by this project.