How many liters of 20% alcohol solution should be added to 40 liters of a 50% alcohol solution to make a 30% solution?
Choose the most appropriate option.
A) 60 liters	B) 70 liters	C) 80 liters	D) 90 liters	E) 50 liters
Let x be the quantity of the 20% alcohol solution to be added to the 40 liters of a 50% alcohol. Let y be the quantity of the final 30% solution. Hence   x   + 40= 
<gadget id="calculator">  + 40</gadget>
<output>40</output>
y   We shall now express mathematically that the quantity of alcohol in x liters plus the quantity of alcohol in the 40 liters is equal to the quantity of alcohol in y liters. But remember the alcohol is measured in percentage term.   20% x + 50% * 40= 30% y   Substitute y by x + 40 in the last equation to obtain.   20% x + 50% * 40 = 30% (x + 40)   Change percentages into fractions.   20 x / 100 + 50 * 40 / 100= 30 x / 100 + 30 * 40 / 100   Multiply all terms by 100 to simplify.   20 x + 50 * 40 = 30 x + 30 * 40   Solve for x.   x = 80 liters   80 liters of 20% alcohol is be added to 40 liters of a 50% alcohol solution to make a 30% solution   Answer 80 liters
<result>C</result>
How many liters of 20% alcohol solution should be added to 40 liters of a 50% alcohol solution to make a 30% solution?