heshamelaziry wrote:Stuart,
I didn't understand your response. I would appreciate it if you could elaborate, since this could save me lots of work.
Is my solution correct ?
From stem: 20M + 25N = 5500
Statement 2: M + N = 250 , with stem --> 20( 250-N) + 25N= 5500 ( Sufficient)
Statement 1: Total N + Total N + 500 = 5500 ------> Total N = 2500 --> total M = 5500 - 2500 = 3000 ---> # of nonmembers = 2500/ 25 = 100, # of members = 3000/20 = 150 (Suffficient)
If you would let me know which part of the response you didn't understand, I can address specific parts.
Basically, here's the most important rule to remember for data sufficiency:
to solve a system with n variables, you need n distinct linear equations.
In this question, we have two variables: M and N
From the stem, we can derive one equation (the one you posted).
Therefore, in order to answer ANY question about the system, we need one more equation.
(1) gives us another equation (as you translated). The only variables are still M and N and the equation is distinct (i.e. different) from the original equation. Equally important, it's linear (there are no exponents other than 1 attached to any variables).
Therefore, (1) is sufficient.
(2) same deal as (1) - also sufficient alone.
Remember, we don't care what the answer IS in data sufficiency; we just care whether we have enough information to get an answer. If you understand the principle, you rarely have to actually do all the math.
