TMUA-P2Y-PRF-003 — Paper P2 · Following proofs · Level 2

Options

1. A
   If $n$ is a multiple of $5$ then $n^2$ is a multiple of $5$; proving it proves the original.
2. B
   If $n$ is not a multiple of $5$ then $n^2$ is not a multiple of $5$; proving it proves the original because a statement and its contrapositive are equivalent.
3. C
   If $n^2$ is not a multiple of $5$ then $n$ is not a multiple of $5$; proving it proves nothing.
4. D
   There exists $n$ with $n^2$ a multiple of $5$ and $n$ not a multiple of $5$; proving it proves the original.

Letters only — the answer key is hidden. Work it out, then check the solution below.

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