Yeah, I personally find it a lot easier to compute 13% of 17, rather than 17% of 13.

I guess it's easy to miss that m% just means ×m÷100

6% of 50 means 50 × 6 ÷ 100, and because multiplication and division have the same order of operations you can switch them around. so it is also equal to 6 × 50 ÷ 100, in which you can simplify 50 ÷ 100 into 1 ÷ 2, but you could always do that: 50 × 6 ÷ 100 = 1 × 6 ÷ 2.

this "shortcut" however is of extremely limited use. basically for taking a percentage of anything other than things that can very easily divide or multiply 100 like 50 in this example or maybe 10 or 500 it's nearly useless.

It's because percent just means ×0.01 and multiplication can be rearranged

So 37 % of 38 is equivalent to (37 * 38 ) / 100 ? Which I can almost do in my head.

37 * 4 is 148 I think, so 37 * 40 is 1480. Subtract 74 we have 1406. So we have 14.06?

Just save the meme in the maths folder!

23% of 53

Probably 5 tbh

is tree fiddy

Yeah my brain just sees 5*6, and then I move the decimal. I never understood how people couldn't figure out tips when they wanted 20%.

If you live in the U.S. you do them quite often, multiply by 2. Want 10 multiply by .1... Half that and add it if you want 15. Whatever is easiest at that moment

I prefer to keep it technically correct yet evil and confusing. 6% being a fancy way to write 0.06 or 6 * 1/100 means we can take 6 * 50 * 1/100 and simplify to 300 * 1/100 and then represent that as 300%.

Or, more generally:

Taking X percent of something is the same as multiplying by X/100.

X percent of Y = Y(X/100)=(YX)/100

Y percent of X = X(Y/100)=(XY)/100

(YX)/100=(XY)/100

Percentages are indeed reversible.

You can also

Multiply one side, divide the other to get the base number to get the base number to 100.

6% of 50 == 3% of 100 == 3

5% of 20 == 1% of 100 == 1

7% of 50 == 3.5℅ of 100 == 3.5

~~14% of 200 == 7% of 100 == 7~~

Edit* as pointed out below, this one was incorrect.

14% of 200 == 28% of 100 == 28

You don't have to stop at percentage either.

25 * 16 = 100 * 4

If you're doing addition, you can add and subtract.

27 + 13 = 20 + 20

Most of the difficulty is in realizing that one number or the other can be brought up to a nice round number, making the equation simple to do in your head. And obviously, just getting to around number on one side doesn't always make it easy on the other side.

I always loved screwing with math problems to make them easier, which is weird, because overall, I don't really care for math.

I also do shit like borrowing a couple of numbers to make the equation easy and then pull them back out.

392 / 4 == (400 - 8) / 4 == (100-2) = 98

376 / 4 == (400-24)/4 =100-6=94

Of course it goes up a level when the remainder isn't evenly divisible. But I still find it's something I can handle in my head.

371 / 4 == (400-29)/4= 100-7¼ =100-7.25=92.75