Multiplying a Double-Digit Number by a Single-Digit Number

a × b

a

4

b

45

	4 × 45 = 180




×	4 5
4
	4 × 40 = 160 4 × 5 = 20



	160 + 20 = 180

Here is a useful way to think of multiplying a double-digit number by a single-digit number. First, think of the two-digit number as two separate numbers. For example, to find

8×73

:

73=70+3

.

The first digit of this number represents the number of blocks of tens and the second digit represents the number of blocks of ones. Then you individually multiply the blocks of tens and ones by the single-digit number:

8×73=8×70+8×3=560+24=584

.

Once you add up the two products you get the answer you would get from multiplying the two starting numbers.