On Tue, Apr 26, 2016 at 3:09 AM, Bill Gosper <billgosper@gmail.com> wrote:
The simplification 6(9) = 6×9 is an example of (choose one) a) associativity b) commutativity c) distributivity.
Now that you've posted the source, we see that the source does not give this as a multiple choice exercise. What the exercise actually says is "use the distributive property to find the produce 5(31)". with the intended solution of something like 5(31) = 5(30 + 1) = 5(30) + 5(1) = 150 + 5 = 155. I don't see anything wrong with this.If asked to find, say 14 * 99, I would certainly do it by calculating 14(100-1) using the distributive law, rather than using the standard multiplication algorithm. The common core certainly has flaws. But it seems to be widely and unjustly criticized for its attitude that there are a multitude of ways to solve any given problem, and an understanding of what's going on can help you find an easy one, rather than simply mindlessly following an algorithm. Much of this criticism comes from people who were themselves taught to mindlessly follow an algorithm, and view any curriculum that teaches anything they did not themselves learn as a waste of time. Andy