Ahmed MS wrote:If everyone was charged the same fee, how many people came?

a. If the fee had been %0.75 less and 100 more people came the club would have received the same amount.
b. If fee had been $1.50 more and 100 fewer people came, the club would have received the same amount.

I think the % in statement 1 should be $.

Say, the fee was $P and n people came.

Statement 1: (n + 100)(P - 0.75) = nP
Hence, 100P - 0.75n - 75 = 0
We cannot find n as we have one equation but two unknown.

Not sufficient

Statement 1: (n - 100)(P + 1.5) = nP
Hence, 100P - 1.5n + 150 = 0
We cannot find n as we have one equation but two unknown.

Not sufficient

S1 & 2 Together: We can uniquely determine n as we have two equations in two unknown.

Sufficient

The correct answer is C.