A solution problem

DanaJ wrote:Source: Veritas Prep

A vat contains 1,000 liters of a liquid containing 14% magnesium by volume. If half of the water in the vat evaporates, the remaining liquid is approximately what percent magnesium by volume?

A) 20%
B) 22%
C) 25%
D) 28%
E) 30%


Experts: only Veritas Prep experts, please!

IOM C 25%

860 lt Water+140 lt Mgn = 1,000 lt Liquid

430 lt Water evaporates => 430 lt Water+140 lt Mgn= 570 lt Liquid;

140 lt Mgn/ 570 lt Liquid =~ 25% Mgn concentrate

OA is C.

Nice work by Night Reader.

Solution: At 1,000 liters, the liquid is currently 140 liters of magnesium and 860 liters of water. If half of the water evaporates, we now have 430 liters of water. The amount of magnesium is constant, so we have 570 total liters, of which 140 are magnesium. 140/570 isn't an easy calculation, but since we are looking for an approximate percent, we can round it to 140/560, or 25%, which is answer (C).