Wrong solution.

[SCSmith]

A solution of gasoline and oil used for a gas powered weed trimmer is 8% oil. How much gasoline must be added to 3 gallons of the solution to obtain a new solution that is 5% oil?

.08x = .05(x + 3)
.08x = .05x + .15
.03x = .15
x = 5 gallons.

The correct solution is 1.8 gallons.

 

[Unco]

G'day, SCSmith.

The initial volume is 3 gallons, so the left-hand side should be 0.08 * 3.

 

[Denis]

The 3 gallons = 92% gasoline (100 - 8)
Added is 100% gasoline to get solution = 95% gasoline (100 - 5)

3 @ 92
x @ 100
======
3+x @ 95

(3*92 + 100x) / (3+x) = 95 : ok?