Evaluate 15% of 80% of 90

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