You can take 1% of anything, then multiply as well.

Like 7% of 15.50

1% is .155 (10% is moving decimal to left once, 1% is twice)

.155 × 7 = 1.083

That's a hard one to do in your head, but .155 × 7 is easier to do on paper than 15.50 × .07.

Say something is 49.99 and 7% off. 1% is .5. .5 ×7 = 3.5. You could probably do that in your head. Otherwise, good luck trying to do 7% of 50 in your head.

Edit: Hmm. So you could also do 3.5% of 100 instead of 7% of 50. That would have been the easiest way to do that one.

Bonus: I thought I'd mention 11s. They are my favorite thing in math because they are so easy and you seem like a math wizard to anyone.

Say you have 42 × 11. That's 462.

You just split apart the 4 and 2, add 4 and 2, then stick it in the middle.

Something like 67 × 11. Where the digits add >10.

6...7, 6+7=13, 6+1...3...7. So 737.