Generalising the divisibility tests of 9 and 11

Ramachandran, A. (2019) Generalising the divisibility tests of 9 and 11. At Right Angles (5). pp. 32-33. ISSN 2582-1873

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Abstract

Divisibility tests for 9 and 11 are generally taken up at upper primary school level. The test for 9 seems to remain in people’s consciousness long after they leave school and move on to other things. The assertion that the sum of the digits of any multiple of 9 is itself a multiple of 9 seems to give a mystical aura to the number 9. The test for 11 is more involved and does not seem to be retained as well, but other patterns in the multiples and powers of 11 are widely appreciated.

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Articles in APF Magazines

Authors:

Ramachandran, A.

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