
Unit 7: Numeracy skills
Decimals
Multiplication
When multiplying decimals, do the sum as if the decimal points were not there, and then calculate how many numbers were to the right of the decimal point in both the original numbers - next, place the decimal point in your answer so that there are this number of digits to the right of your decimal point.
Example 1
2.1 x 1.2
Calculate 21 x 12 = 252 There is one number to the right of the decimal in each of the original numbers, making a total of two. We place the decimal point so that there are two digits to the right of the decimal point in our answer.
So, 2.1 x 1.2 = 2.52
Always look at your answer to see if it is sensible. 2 x 1 = 2, so our answer should be close to 2, rather than 20 or 0.2 which would be the answers if you put the decimal point in the wrong place.
Example 2
1.4 x 6
Calculate 14 x 6 = 84 There is one digit to the right of the decomal point, so our answer is 8.4
Check 1 x 6 = 6, so the answer should be closer to 6 than 60 or 0.6
SMILE - Numeracy skills by Tom Frank, Eric Williams and Clare Wright, University of Birmingham Careers Centre adapted by Marion Kelt Glasgow Caledonian University is licensed under a Creative Commons Attribution 3.0 Unported License.