Multiplying Decimals

Multiplying Decimals

GCSE(F),

To work out where the decimal point will go in the answer:

• work out the multiplication without decimals; then

add the decimal place in at the end.

The number of decimal places in the answer is the same as the total number of decimal places in the original two numbers.

Examples

1. Calculate 25.66 x 2.3.

Answer: 59.018

Work out 2566 x 23 = 59018.  There are 2 decimal places in the first number, and 1 decimal place in the second number; 3 decimal places need to go back into the final answer, which becomes 59.018.

2. A sweet shop is working out the cost of its sweets.  The sweets come in 0.36Kg bags.  What is the cost of one bag of sweets, if the sweets cost £3.55 per Kg? Give the answer in pounds and pence.

Answer: £1.28

The question is a multiplication: 0.36 x 3.55.  Work out 36 x 355 = 12780.  There were 2 decimal places in the first number, and 2 in the second: 4 decimal places need to go into the answer: 12780 becomes 1.2780.  The answer is in pounds and pence, so it needs to be rounded to the nearest penny: £1.28.