Answer:
I’m going to generalise the answer in the hope of preventing a billion questions with the % changed a little.
If you have a calculator X% just means multiply by X and divide by 100.
If you don’t have a calculator or paper handy, you can split the problem: I’ll do it for 25% but in this case the other answers are simpler.
25%=10%+10%+5%.
Now 10% is easy, just move the decimal one place to the left, for instance 35 becomes 3.5.
5% is half of 10% 3.5/2=1.75
Add it all up: 3.5+3.5+1.75= 8.75. Done.
You don't even need to know multiplication above 5x tables, for instance
37% is 10%+10%+10%+7% but that requires multiplying by 7.
37% is also 10%+10%+10%+10% -3% only requiring 3x table.
I'm not sure if this is what you mean but here ya go