math word problem

Question

a 30% solution of fertiliser is to be mixed with a 60% solution of fertiliser in order to get 180 gallons of a 50% solution. how many gallons of the 30% solution should be mixed

Answer 1

a + b = 180

.3a + .6b = 180(.5)

 

a = 180 - b

.3(180 - b) + .6b = 90

54 - .3b + .6b = 90

.3b = 36

b = 120

 

a = 180 - 120 = 60