Multiplying by doubling and halving

There are cases when you’re multiplying two numbers together and one of the

numbers is even. In this case you can divide that number by two and multiply the

other number by 2. You can do this over and over until you get to multiplication this

is easy for you to do.

Let’s say you want to multiply 14 by 16. You can do this:

14×16 = 28×8 = 56×4 = 112×2 = 224.

Another example: 12×15 = 6×30 = 6×3 with a 0 at the end so it’s 180.

48×17 = 24×34 = 12×68 = 6×136 = 3×272 = 816. (Being able to calculate that 3×27 =

81 in your head is very helpful for this problem.)