Bunuel wrote:
If x = 0.rstu, where r, s, t, and u each represent a nonzero digit of x, what is the value of x ?
(1) r = 3s = 2t = 6u
(2) The product of r and u is equal to the product of sand t.
There are times when you can find the question confusing, the underlying math principles escape you, you just can't clear your head about how to tackle the question, or some combination of all three.
At those times, "Brute Force" method comes in handy. Don't use any formulas or cleaver methods to solve. Just apply what the question tells you.
(1) r = 6u: Well there are only two single digit numbers that have that relationship 6 and 1. So, r = 6 and u = 1. Which means s = 2 and t = 3.
SUFFICIENT
(2) r*u = s*t: Can we think of more than one example where that can be true. There's the example above 6, 2, 3 ,1 and there's also 8, 4, 2, 1. But not only that, we can rearrange the numbers to be 1, 3, 2, 6 and 1, 2, 4, 8.
INSUFFICIENT