Apicture that is 3 in. wide and 5 in. high is to be enlarged so that the height will be 12.5 in. what would the enlarged width measure?
a. 7.5 in.
b. 8 in.
c. 8.5 in.
d. 9 in.

A 7.5 12.5÷5=2.5 2.5×3=7 5

We have 20% and 70% salt solutions.
We need 9 liters of 50% salt solution.
"t" is liters of twenty % solution "s" is liters of seventy % solution

A) t + s = 9
B) .2t + .7s = (.5 * 9)
Multiplying A) by -.2
A) -.2t + -.2s = -1.8 Adding that to B)
B) .2t + .7s = (.5 * 9)
.5s = 2.7
s = 5.4 liters of 70% salt

A) t + 5.4 = 9

t = 3.6 liters of 20% salt

Source:
http://www.1728.org/mixture.htm