logitech wrote:If t and u are positive integers, what is the value of t^(-2)u^(-3) ?
(1) t^(-3)u^(-2) = 1/36
(2) t(u^(-1)) = 1/6
(1) let's start by making this less complicated.
t^(-3) is just 1/t^3... u^(-2) is just 1/(u^2).. so, we have:
(1/t^3)(1/u^2) = 1/36
taking the reciprocal of both sides:
(t^3)(u^2) = 36
Since we know that t and u are positive integers, we should be suspicious that there are limited possibilities. Let's break 36 down to primes:
36 = 2*2*3*3
Well, there's no way we're getting an integer cubed by using primes. Therefore, the only possible value for t is 1. Once we know that t has to be 1, u must be 6.
Since we know the values of t and u, we can answer any question about them: sufficient.
(2) simplifying, we get:
t/u = 1/6
Well, there's an infinite number of positive integers (e.g 1/6, 2/12, 3/18, ...) that fit that ratio and, since t and u appear in a different ratio in the question, each set of numbers will give us a different answer: insufficient.
(1) is sufficient, (2) isn't: choose (A).