Question

How many quarts of pure antifreeze must be added to 20 quarts of a 45% antifreeze solution to obtain a 75% antifreeze solution?

Answer 1

24 quarts

Explanation:

45% of 20 is 0.45 * 20 = 9

So in 20 quarts, 9 is pure antifreeze

suppose we want to add x quarts and this will make it 75%. So we can write:

`(9+x)/(20+x)=0.75`

Now we cross multiply, do algebra, and solve for x:

`(9+x)/(20+x)=0.75\\(0.75)(20+x)=9+x\\15+0.75x=9+x\\15-9=x-0.75x\\6=0.25x\\x=(6)/(0.25)\\x=24`

Hence, 24 quarts should be added