If n is a positive integer, for which of the following would the units digit always be equal to the units digit of n?

I. n^5

II. n^10

III. n^25

Correct answer marked below

I only

II only

III only

I and III only

Correct

I, II, and III

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What this question tests

Your command of divisibility, primes, factors, parity, and how the GMAT tests properties of integers.

Forgetting that 1 is not prime, that 0 is divisible by every integer, or that negative numbers flip your assumptions.

If n is a positive integer, for which of the following would the units digit always be equal to the units digit of n?I. n^5II. n^10III. n^25