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Is y^3 divisible by 9?

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Source: — Data Sufficiency |
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Answer Explantion

by siddogg » Wed Oct 28, 2009 11:28 pm
The answer states that if y^3 is divisible by 9, y must be divisible by 3.

How can you intuitively arrive at this conclusion (I agree this is true, but would never have arrived at this conclusion)? And more importantly, are there any other extensions of these divisibility/exponent rules?

Ans. B
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by bln123 » Thu Oct 29, 2009 1:08 am
If y^3 is divisible by 9 then multiples of y will also satisfy the formula.

4^3 is 64 and therefore has a cross sum of 10 -> not divisible by 9

6^3 is 216 and therefore has a cross sum of 9 -> divisible by 9 -> B is correct
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