Solution question - Solution X is 15% sugar by volume ...

[Brent@GMATPrepNow]

Solution X is 15% sugar by volume, and Solution Y is 20% sugar by volume. 200 milliliters of Solution X is mixed with 400 milliliters of Solution Y to create a new mixture. If 100 milliliters of water evaporates from the new mixture. the resulting mixture will be what percent sugar by volume?
(A) 18
(B) 19
(C) 20
(D) 21
(E) 22

Please note that this is not an official GMAT question; it’s my attempt to create mid-range (500 to 650-level) GMAT-style questions for this forum.

[codesnooker]

Answer should be 22%

30ml sugar in 200ml solution X
80ml sugar in 400ml solution Y

110ml sugar in 600ml solution XY

After evaporation, resulted solution is 110ml sugar in 500ml solution of XY.

that is volume of sugar in solution = 22%

[Brent@GMATPrepNow]

Answer should be 22%

30ml sugar in 200ml solution X
80ml sugar in 400ml solution Y

110ml sugar in 600ml solution XY

After evaporation, resulted solution is 110ml sugar in 500ml solution of XY.

that is volume of sugar in solution = 22%

Nice work.
For more complex questions, I like to sketch the mixtures with their components separated. Here's what I mean: