Double or triple, makes any difference?

I've written an integer on a piece of paper.

I notice that

  • if I double the value, it will be divisible by 3;
  • if I triple the value, it will be divisible by 2.

Which of the following could be the integer that I've written?

2018 2019 2020 2021 2022

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2 solutions

Geoff Pilling
Oct 22, 2018

The first statement implies it is divisible by 3. The second statement implies it is divisible by 2.

Therefore we need a number divisible by 6.

2022 \boxed{2022} fits the bill!

Naren Bhandari
Nov 3, 2018

Say M M be the written integer then { 2 M 3 = M M 3 ( 1 ) 3 M 2 = M M 2 ( 2 ) \begin{cases}\dfrac{2M}{3} = M-\dfrac{M}{3} \cdots (1)\\\dfrac{3M}{2} = M-\dfrac{M}{2}\cdots (2) \end{cases} now subtracting equations we have M 2 × 3 \dfrac{M}{2\times 3} . Rather than checking than all the cases we can directly go for the number divisible by 3. 2019 2019 and 2022 2022 are possible cases(divisibility rule of 3) thus only solution is 2022 2022 .

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