Percentages without the head scratching
Most percentage questions are one of a few types: how much is 15 percent of 80, what percent is 12 of 48, how much did a price change, what is a price after adding tax or removing a discount, and what was the price before tax was added. Each has its own card with the numbers built into the question, so you type them where they belong and read the answer at once.
Under every result, a sentence states it in plain words, for example that going from 80 to 100 is an increase of 25 percent. That makes it easy to copy into a report or check homework.
Common traps
A 20 percent increase followed by a 20 percent decrease does not bring you back to the start: 100 becomes 120 and then 96. And to remove tax from a price, divide by 1 plus the tax rate instead of subtracting the percentage: 120 including 20 percent tax was 100 before tax, not 96. The last card does exactly that.