this post was submitted on 12 Nov 2024
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You can remove the decimal then add it back at the end
15.50
Is
1500
Half would be 775
Or 7.75
yep, and figure out what 20% of your bill is by taking 10% and double it. saves my ass every time i gotta tip lol
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.