sud21 wrote:There are some green balls and blue balls in a box. what is the total number of the balls?
1) The number of the green balls is 1/3 of the number of the total balls
2) If one green ball is taken out, the remaining green balls are 1/5 of the balls in the box.

Let G = # of green balls
Let B = # of blue balls

Rewrite target question as "What is the value of G + B?"

Statement 1:
G = (1/3)(G+B)
To simplify, multiple both sides by 3 to get: 3G = B+G
Simplify to get: 2G-B = 0
Since we cannot find the value of G+B, statement 1 is NOT SUFFICIENT

Statement 2:
G-1 = (1/5)(G-1+B)
To simplify, multiple both sides by 5 to get: 5G-5 = G-1+B
Simplify to get: 4G-B = 4
Since we cannot find the value of G+B, statement 2 is NOT SUFFICIENT

Statements 1 & 2:
We now have two equations (2G-B = 0 and 4G-B = 4), which we could solve for G and B
As such, we now have SUFFICIENT information to find the value of G+B

Answer = C

Cheers,
Brent