Question:
Find the smallest integer n such that 840n is a perfect square.

Approach:
First, express 840 as a product of prime factors, i.e. (2^3)(3)(5)(7).

Next, we must consider two facts:
1. Any perfect square must have powers which are divisible by 2.
2. 840n must have prime factors 2, 3, 5 and 7.