Calculation Shortcuts

When I originally wrote this page, I promised that more shortcuts would appear here "shortly". I then promptly proceeded to forget completely about this page for several months. I do intend to complete this page but I won't promise when.

One method of being able to do multiplication in you head is to break the problem up into more managable parts. Suppose I asked you what 59 × 43 was. One way of solving this problem is to remember that 59 is (60 - 1), so 59 × 43 is just 60 × 43 - 1 × 43, or 10 × (6 × 43) - 43. Now the only complicated multiplication is 6 × 43, and it's not too hard - just think (6 × 40 + 6 × 3) which is 258. So the answer to the problem is 2,580 - 43 = 2,537. Of course, you'd do all of the above in your head. If I punch in 59 × 43 on my calculator, I get 2,537. Neat, eh?