It should be 40 percent.
You can think of it as starting with 100 as in 100 dollars or 100 tic tacs
If you take away 25%, you take away 25 tic tacs and now you only have 75.
From your 75, you take away 20% which is equal to 15. 75- 15=60
If you look at the end result of 60, you can see that that is 100 - 40 so 40% of the total was taken off