06-12-2017, 11:32 AM
Tony - I recommend a listen to the inimitable Tom Lehrer singing 'New Math' in about 1965. It explains everything. This is just a taste of the opening lines:
Consider the following subtraction problem, which I will put up here: 342 - 173.
Now remember how we used to do that. Three from two is nine; carry the one, and if you're under 35 or went to a private school you say seven from three is six, but if you're over 35 and went to a public school you say eight from four is six; carry the one so we have 169, but in the new approach, as you know, the important thing is to understand what you're doing rather than to get the right answer. Here's how they do it now.
You can't take three from two,
Two is less than three,
So you look at the four in the tens place.
Now that's really four tens,
So you make it three tens,
Regroup, and you change a ten to ten ones,
And you add them to the two and get twelve,
And you take away three, that's nine.
Is that clear?
Etc etc
p.s. I could never follow it either!
Consider the following subtraction problem, which I will put up here: 342 - 173.
Now remember how we used to do that. Three from two is nine; carry the one, and if you're under 35 or went to a private school you say seven from three is six, but if you're over 35 and went to a public school you say eight from four is six; carry the one so we have 169, but in the new approach, as you know, the important thing is to understand what you're doing rather than to get the right answer. Here's how they do it now.
You can't take three from two,
Two is less than three,
So you look at the four in the tens place.
Now that's really four tens,
So you make it three tens,
Regroup, and you change a ten to ten ones,
And you add them to the two and get twelve,
And you take away three, that's nine.
Is that clear?
Etc etc
p.s. I could never follow it either!