In this activity, we will multiply numbers by 0.1 and 0.01.
When you multiply by 0.1, you are simply dividing by 10.
When you multiply by 0.01, you are simply dividing by 100.
15.1 × 0.1 = 15.1 ÷ 10 = 1.51
0.123 × 0.01 = 0.123 ÷ 100 = 0.00123
When multiplying with decimal numbers, we need to count how many decimal places we have in our calculation and make sure that we have the same number in our answer!
In the first example above, we have two decimal places in the calculation: 15.1 x 0.1, so our answer must have two decimal places: 1.51
In the second example, we have five decimal places in the calculation: 0.123 x 0.01, so our answer must have five decimal places: 0.00123
If you remember this rule about decimal places, you'll find multiplying decimals becomes really simple.
Let's have a go at some questions now.