Multiplying a 2-digit number by 45

1. Select a 2-digit number.
2. Multiply it by 5.
3. Add a zero.
4. Find the difference between these two numbers

   Example:

1. The 2-digit number chosen to multiply by 45 is 54.
2. 5 x 54 = 270.
3. Add one zero: 2700.
4. Subtract: 2700 - 270 = 2430
   (subtract left to right: 2700 - 200 - 709 = 2500 - 70 = 2430)
5. So 54 x 45 = 2430.

   See the pattern?

1. If the number to be multiplied by 45 is 27:
2. 5 x 27 = 135
   Think 5 x 27 = (5 x 20) + (5 x 7) = 100 + 35 = 135.
3. Add one zero: 1350.
4. Subtract: 1350 - 135 = 1215
   (subtract left to right: 1350 - 100 - 30 - 5 =
   1250 - 30 - 5 = 1220 - 5 = 1215)
5. So 27 x 45 = 1215.

Practice - especially the subtraction - and you will become adept at finding these products.