Why YSK: It helps when calculating percentages. If you want to find out what 2% of 20 is, do 20% of 2 instead and you’ll get 0.4. So, 2% of 20 also equals 0.4.
Or, 12% of 25 can be alternatively written out as 25% of 12 instead, which would be 3.
Explanation: Commutative Property. So, 0.07 times 50 will always equal 50 times 0.07
Okay this is something everyone should know. Great tip!
This isn’t the only property that makes mental math easy. What is 3.5% of 62? Inverting the percentages doesn’t really help but if we realized 3.5% = 1%+1%+1%+0.5% we have some easy math. This gives us 0.62+0.62+0.62+0.62/2=2.17
Also remember there isn’t a teacher sitting over your shoulder to check your work, most of the time you do mental math, getting close is good enough. 62 is close to 60 and 3.5% is close to 4, and 60 x 4% is easy math to get an answer that will be a little less than 2.4.
Percentage is just a fancy form of decimal point. I just multiply them together then move decimal digit to the left twice.
damn all these good tips for doing quick percentage math @.@
This is true for quite a few other things as well. For instance, “hertz” really just means “per second”. However, it’s easier to write/type “Hz” instead of “s^-1”.
Proof:
(x/100) * y = xy/100 = (y/100) * x