# YSK that X% of Y equals Y% of X. So, if you want to find out what 9% of 50 is, you can instead find out what 50% of 9 is, which is 4.5. This means that 9% of 50 is also equal to 4.5.

Another example: 12% of 25 is equal to 25% of 12, which is 3. This also means that 12% of 25 is equal to 3.
An alternative method to calculating percentages is to multiply the two numbers \(so you would multiply 50 and 9\) and then divided by 100. So 50 times 9, and then divided by 100 would still yield the same result, which is 4.5.
You should know how to do percentage problems like this in case you ever have to calculate the tax of something or if your profession requires you to know percentages well.

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But it helps nothing when o have to do 7.893% of 23.3045

Ah neat, a math post. Never hurts to plug-in the divisibility rules might help someone: * 1 - *is always divisible by one* --- * 2 - *the unit's digit is divisible by two* (0, 2, 4, 6, 8) --- * 3 - *the sum of the digits should be divisible by 3* >[81 gives 8+1=9 which means it is also divisible by 3] --- * 4 - *the last 2 digits should be divisible by 4* >[84412516 has **16**, hence divisible] --- * 5 - *the last number should be a 0 or 5* --- * 6 - *it should be divisible by both 3 and 2* [see above] --- * 7 - *slightly tricky* >Just take the last digit, double it, and subtract from the rest of the digits. >eg. 336 >6x2=12 >33-12=21 >**21** which is divisible by 7, hence your answer --- * 8 - *the last 3 digits are divisible by 8* >[3893048, we get **048** hence it's divisible] --- * 9 - *the sum of the digits should divisible by 9* --- * 10 - *it ends in 0* --- --- ^(feel free to point out any mistakes I may have made or any better rule you have in mind)

Now that's some useful shit!

or- first find the 10% of 50 - which is 5 , and then find what 1% of 50 is - which is 0.5 , and then subtract 10%-1% -- 5-0.5 9% -- 4.5

Big, if true!

Repost but still helpful

God bless u...

So, 17% of 34 is a little over 1/3rd of 17. But that's...?

Protip: "X of Y" almost always means "X times Y".

You can also do 0.73 * 723 if you want 73% percentage of 723, which is 527.79. Or if you want to work out a percentage increase of something (e.g. 73% increase of 723) just do 1.73*723 = 1,250.79

Haha, nice. It turns out it doesn't matter in which order you multiply numbers!

OMG I remember this life pro tip! It was a life pro tip not too long ago!

I work in a cardboard box factory where you constantly have to do on the fly division. Like if 2250 pieces go into a unit and they’re in bundles of 25 pieces you have to figure out how many bundles go in a layer and how many layers are in a stack etc... this is more helpful than you will ever realize. Thank you from the bottom of my heart

Yes, I had an interview question some years ago that explored this. Needless to say, I did not get the job.

holy shit

When I worked in retail this YSK was particularly handy for reduced goods. Not always, but quite often. Like, if we had a set of 4 mugs, for £5, and 1 mug was smashed, and a customer wanted to buy the remaining 3 mugs (75% of the original product), rather than figure out 0.75*5, it was easier to figure out 75p*5 (or 75*2*2+75) in my head. We had calculators, but when you do this often you get quite fast at it, and start to memorise certain recurring discounts, only using the mental maths as a double check as you ring in the sale.

Dunno how good this way is and it probably doesn't work with decimals but if you're good in multiplication you can just do 9*5 and add the decimal point in

yea or 9x5 = 45 and move the decimals properly (2 to the left due to %, and 1 to the right due to the 0 in 50)

Also, if you need to know a percentage of a number, say 30% of 77, where the percentage ends with a zero (10%, 20%, 30% , 40%, etc.) -Just use the decimal of said percentage (0.3 in this example) -Move the decimal over to the right (3.0) -Mulitply with the number your looking for a percentage of, which in this case would be 77 times 3.0 which would be 231.... -Then move the decimal back accordingly and you figure out 30% of 77 is 23.1. Sorry if I didn't explain that more in depth or correctly, I just woke up and have not had any coffee yet..... Also, if this is obvious or known to you, it's not the same for everyone.

Oh no I’ve gone cross eyed

My brain got tongue twister reading this

You should know that they teach cross multiplication in 8th grade.

Oh look, this post again