To do this, you need to work out the percentage value 15 is (40-25)
You divide 100 by 40 to find out the percentage of 100 one is.
100 / 40 = 2.5,
Then multiply 15 by 2.5 to work out the percentage change:
15 * 2.5 = 37.5.
The percent discount is 37.5%
Hope this helps!
