<PRE><B>Question 124104</B>
 how many liters of water must be evaporated from 10L of 40% salt solution to produce a 50% solution 
:
Let x = amt to be evaporated
:
write a salt amt equation
(the amt of salt remains the same only the amt of water changes, thus changing the percent)
:
.40(10) = .50(10-x)
4 = 5 - .5x
+.5x = 5 - 4
1x = 2(1); multiply equation by 2 to get rid of the .5x 
x = 2 liters of water has to be evaporated

;
:
Check for equality
.4(10) = .5(10-2)
4 = .5(8)</PRE>