Mental Math Can Make You Unstable

My grandson, Maverick, is in the 3rd grade. I have been working with him on learning his multiplication facts by using a times table and the like. We make a little game of it and even use flash cards from time to time. He thinks those tools for learning are a bit old fashioned. I am trying to keep an open mind to new kinds of instruction. I try to be careful not to launch into any "when I was your age..." examples.

The math worksheets he brings home talks about using "Mental Math." I think this is akin to what our teachers used to mean when they said, "Do the work in your head." In the examples they want you to round up to the nearest 10 and then add or subtract the number and "work it out."

Huh?

Let me show you how this kind of calculation looks on paper. Here is your problem: 73 - 58 = __

Using "Mental Math" here is how you "work it out":
73 - 58 = __
73 - 60 = 13
13 + 2 = 15
73 - 58 = 15

I guess it is easier to subtract when one number is a ten and then add back the number you rounded and then that is the answer to the original problem....but try to explain that to a 3rd grade boy. I was able to figure out how the exercise went but trying to get Maverick to "work it out" was quite an exercise in itself.

I guess these mathematics torture chamber exercises are trying to show what you are doing in your head when you are working it out in your head. It just seems easier to say, " Borrow from the 7, subtract 8 from 13 to get 5, subtract 5 from 6 to get 1. The answer is 15."

I know he will get this math mastered and will learn to love working with numbers. And therein lies the problem. Now I am worrying he will grow up to disgrace the family by being an investment banker who works on Wall Street!