Here are a couple of math facts that not everyone apparently understands.
If you do, forgive me. I’m not implying this is groundbreaking mathematics.
Percentages (and ratios) are reversible
This means that 24 percent of 50 is the same as 50 percent of 24.
I showed this to someone last week, and it blew their minds.
But it’s true, and in many cases, it makes percentages — like the one above — much easier to calculate.
50 percent of 24 (12) is much easier to calculate than 24 percent of 50 (also 12, but
You can subtract without regrouping by simply using negative numbers.
So yes, a problem like 57 – 28 = x can be solved by regrouping (shown below).
But you can also subtract the digits in the ones column (7 – 8 = -1) and the tens column (50 – 20 = 30).
Then you’re left with 30 – 1 = 29.
I subtract using this method quite often.
I showed this to teachers at a training session years ago, and it blew their minds.
