This is a pic going around on Facebook, usually accompanied by several people ranting. I couldn’t understand it myself when I first saw it. I asked my brilliant daughter-in-law and also googled. Now, I get it.
Beginning at 12, we increase either by 5s, 10s, and finally by 1s. This is a way to understand exactly what the numbers are doing instead of using rote memorization.
Here we begin at 12. To get to fifteen, we add 3. Now, to get to 20, add 5 more. To get to 30, add 10 more. Now, we’re close to our goal of 32. We have 3, 5, and 10 for a total of 18. To reach 32, add 2 more to receive our answer of 20.
It’s a way of looking at subtraction from a different angle.
I would probably do it this way:
12 + 10 = 22
22 + 10 = 32
Answer = 20