Multiplying decimals · Usually met around P5
Rounding decimals
Exact product first, round at the end.
How to do it
Method
Exact product first, round at the end
2.35 × 1.7 = 3.995 ≈ 4.0
Another way
Number line
2.963 is between 2.9 and 3.0, nearer 3.0
In full
To round to one decimal place, look at the hundredths: 0 to 4 rounds down, 5 to 9 adds 1 to the tenths; to two places, look at the thousandths. 2.96 to one place: the hundredths digit is 6, so round up; 9 + 1 = 10 carries into the ones, giving 3.0 (written 3.0 to show it is to one place). “≈” means about equal: 3.14159 ≈ 3.14. In a multiplying problem, work out the exact product first and round only at the end; rounding the numbers first can give a wrong answer. Or think of a number line: 2.963 lies between 2.9 and 3.0 and is closer to 3.0.
Worked examples
Have a go first, then open each one for the answer and the working.
Example 1
Round 76.605 to one decimal place: about □
Show the answer and working
Answer: 76.6
Look at the hundredths, 0: 0–4 down, 5–9 up. 76.605 ≈ 76.6.
Example 2
Round 86.2428 to two decimal places: about □
Show the answer and working
Answer: 86.24
The thousandths digit, 2, decides the hundredths: 86.2428 ≈ 86.24.
Example 3
4.318 ≈ 4.3 (rounded to one decimal place)
True or false?
Show the answer and working
Answer: True
Round on the hundredths: to one place, 4.318 is 4.3.
Practise it in the game →Multiplying decimals · Free to start, unlimited questions, no download