First you find 80% of 90. Set up the proportion: 80 X —— = —- 100 90 I’m simplifying the 80/100 so it’ll be easier to solve: 4 X — = —- 5 90 Then cross multiply: 4(90) = 5x 360 = 5x x = 72
So 80% of 90 is 72. (Or you could have multiplied 90 by 0.8 as a shortcut). Now you find 15% of 72. You can either multiply 72 by 0.15 or set up the proportion like this: 15 X —— = —- 100 72 Cross multiply and solve. You should get 10.8
