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 ...

Now that we've learned the basics of lightning fast mental addition, mental subtraction, and mental multiplication, it's time to turn our attention to a few tips that will help you take your skills to ...