• Sludgeyy@lemmy.world
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      11 days ago

      You can remove the decimal then add it back at the end

      15.50

      Is

      1500

      Half would be 775

      Or 7.75

      • cheers_queers@lemm.ee
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        11 days ago

        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

        • Sludgeyy@lemmy.world
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          10 days ago

          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.