Adding and subtracting decimals
- Line up the decimal points, and fill any gaps with zeros: 8 − 2.35 is 8.00 − 2.35 = 5.65.
Multiplying decimals
- Ignore the decimal points and multiply, then count the total number of decimal places in the question and put that many in the answer.
- 0.3 × 0.2: 3 × 2 = 6, and there are 2 decimal places, so the answer is 0.06.
- Multiplying by a number between 0 and 1 makes the answer smaller.
Dividing decimals
- Make the divisor a whole number by multiplying both numbers by 10, 100…: 4.8 ÷ 0.2 = 48 ÷ 2 = 24.
- 7.2 ÷ 0.08 = 720 ÷ 8 = 90.
- Dividing by a number between 0 and 1 makes the answer bigger.
Terminating and recurring decimals
- A terminating decimal ends, such as 1/4 = 0.25.
- A recurring decimal repeats forever, such as 1/3 = 0.333…, shown with a dot over the repeating digit.
Using a known fact
- If 48 × 32 = 1536, then 4.8 × 0.32 = 1.536: there are three decimal places in the question.
Key terms
- Decimal place
- A digit after the decimal point.
- Terminating decimal
- A decimal that ends.
- Recurring decimal
- A decimal with digits that repeat forever.
- Divisor
- The number you are dividing by.
- Dividend
- The number being divided.