19 is only 1 away from 20, so you prefer to start by multiplying 20 times 5, which equals 100. Then we need to take away a squadron of 5, because there are actually only 19 squadrons, not 20. 100 take ...

NARRATOR: Yes, that is quite a hard sum. It might be easier if we separate the 17 into a 10 and a 7, and the 14 into a 10 and a 4. That gives us a 10, a 10, a 7 and a 4. Let's start by adding the ...

Math scores in the U.S. have been so bad for so long that teachers could be forgiven for trying anything to improve them.

Math scores in the U.S. have been so bad for so long that teachers could be forgiven for trying anything to improve them. Unfortunately, many of the strategies they’re using ...