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Calc tip quickly in your head

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That's how I have done math in my head since I was 6.

101 x 101 = 100 x 101 + 101 = 100 x 100 + 100 + 101 = 100 x 100 + 100 + 100 + 1

10,000 + 200 + 1 is easier to do in your head than 101 x 101

Normal people are probably still moving down to the second line and putting down the 0 like they were taught in school in their head and failing to remember what they "wrote down" previously when it comes time to add it all up.

Of course this example could be done fast the traditional way when you see that its just 10,100 + 101 but that's not always the case.


All they teach in school is the slow human way of doing math sequentially with carrying and doing ones, tens, hundreds individually. If you break down into multiple parts by place and use a parallel multiply and accumulate process like a computer its much more effective.

The school method is impossible to do in your head because human short term memory sucks for long carry chains.
 
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Tweak155 said:
If you can't realize it is $7 and not $70 on a $35 bill then you shouldn't spend money period. You need a step 2 to move the decimal? Even then it is less "work" than your method.
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lol...yea, i figured to mistyped...

are all your bills always even amounts? do you based your food purchases off of what will equal whole numbers including tax?

you picked an easy one, $35 even. do the same for a typical bill in your head. I'm guessing you use a calculator. Not to mention the fact that not everyone tips at 20%, when 15% is customary. If you want to give more money away, that's your choice.

"my method" takes seconds in my head. it seems it's not just "my method" either.

Finding 10% takes almost no time, then it's easy math to the % tip you want.
 
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Is third grade division by a single digit too hard? Average, divide by 6. Good, divide by 5. Very good, divide by 4.
 
DrPizza said:
Is third grade division by a single digit too hard? Average, divide by 6. Good, divide by 5. Very good, divide by 4.
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I'm scared by the math some people do.

Its a 15% tip, just multiply it by .15. Its not that hard. If your brain can't handle that, round it. Round the tip down to the next $5, multiply it by .2 and then round down to the nearest dollar. It will get you close enough.

So bill is $22. Round it down to $20. 20% of $20 is $4. 15% of $22.00 would have been $3.30. You are close enough and didn't have to hurt your brain.

This is pretty much what I do except I round up. So a $22 bill would get a $5 tip.
 
ch33zw1z said:
lol...yea, i figured to mistyped...

are all your bills always even amounts? do you based your food purchases off of what will equal whole numbers including tax?

you picked an easy one, $35 even. do the same for a typical bill in your head. I'm guessing you use a calculator. Not to mention the fact that not everyone tips at 20%, when 15% is customary. If you want to give more money away, that's your choice.

"my method" takes seconds in my head. it seems it's not just "my method" either.

Finding 10% takes almost no time, then it's easy math to the % tip you want.
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So it is easier to move a decimal, divide by 2 (how far off from this is multiply by 2?), then add it to the original number than it is to multiply by 2 and move a decimal?

Not to mention, what number under ~$50 (probably typical average high for 2 people?) can you not multiply by 2 instantly in your head?

My method doesn't even take a second in my head, does that mean it is better?

If $35 is such an easy number, you tell me if it takes you longer to multiply by 2 or move the decimal, divide by 2 then add it to the original number.
 
Out of curiousity, don't they teach practical math shortcuts in elementary school anymore? If not time for you to fire up the google.
 
zinfamous said:
cheap tip.

why make things that complicated when it is so much easier?

take the tax.
double the tax.
there is your tip.

that will generally work out to about 17-18% in most states.
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Where do you live? 17 or 18% seems crazy!

Here in Ontario, its 13% on nearly everything you buy. Way more than that on gas, alcohol, and cigarettes though.
 
SparkyJJO said:
You must have high taxes.

Only recently did we break 7% sales tax here in Ohio, which I'm a tad bit miffed about.
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<--examine location. 😀

cbrunny said:
Where do you live? 17 or 18% seems crazy!

Here in Ontario, its 13% on nearly everything you buy. Way more than that on gas, alcohol, and cigarettes though.
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oh, the calculation I gave is the tip percentage--17% plus. when you double the tax charge, you end up with that proper percentage for tips.

tax is 9% here....I think.
 
Uhh, duh? I always just take 10%, double that, then decide what round number I want to fall at in between based on service level (round down closer to 10% for normal service, up closer to 20% for good service, close to 15% regardless unless it was spectacularly good or bad).
 
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