this post was submitted on 12 Nov 2024
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Decimals are the devil's work.
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.