Three questions, one calculator — and it shows the working so you can do the next one in your head
Most percentage calculators give you a number and nothing else. This one shows the route as well, because the route is the part worth keeping: once you can see that a percentage is just 1% multiplied up, most everyday percentages stop needing a calculator at all.
Multiply the number by the percentage and divide by 100. For 15% of 60: 60 × 15 ÷ 100 = 9. In your head, find 10% (6), halve it for 5% (3), and add them.
Divide the part by the whole and multiply by 100. 9 out of 60 is 9 ÷ 60 = 0.15, which is 15%.
Subtract the old value from the new one, divide by the old value, then multiply by 100. From 40 to 50: 10 ÷ 40 = 0.25, which is a 25% increase.
Because each percentage is taken from a different starting number. 100 rises 20% to 120, then falls 20% of 120 — which is 24 — leaving 96, not 100.
Build them from 10% and 1%. 17% is 10% + 5% + 2%, and each of those is one easy step from the 10% you already found.