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

  • Flyingtiger188@kbin.social
    1·
    1 year ago

    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.

  • zephyr@lemmy.world
    0·
    1 year ago

    Percentage is just a fancy form of decimal point. I just multiply them together then move decimal digit to the left twice.

    • stallmer@lemmy.oneEnglish
      1·
      1 year ago

      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”.