math question need help

Question

A chemical company makes two brands of antifreeze. The first brand is 65%

 pure antifreeze, and the second brand is 90%

 pure antifreeze. In order to obtain 110

 gallons of a mixture that contains 70%

 pure antifreeze, how many gallons of each brand of antifreeze must be us

Answer 1

Let S = gal of 65% and N = gal of 90%

S + N = 110

.65S + .9N = 110*.7

Multiply the 2nd equation by 100 and divide it by 5 (or multiply by 20)

13S + 18N = 1560 (equation 3)

Multiply the 1st equation by 13

13S + 13N = 1430 (equation 4)

Now subtract equation 4 from equation 3...and you solve it from there!