Rounding decimals

Rounding using rules

We can round numbers using conventions or rules for rounding. We refer to the digit to be considered as the rounding digit. For example, if the number 3.168 is to be rounded to 2 decimal places then 6 is the rounding digit.

• If the digit following the rounding digit is 0, 1, 2, 3 or 4 the rounding digit stays the same.
• If the digit following the rounding digit is 5, 6, 7, 8 or 9 the rounding digit will increase by 1.

When the rounding is completed, the digits following the rounding digit are discarded.

Following this convention 3.168 is 3.17 when rounded correct to 2 decimal places.

Illustrating rounding using a number line

Question 1

Round 6.72 correct to 1 decimal place (tenths).

Solution

• 7 is the rounding digit.
• 6.72 lies between 6.70 and 6.80.
• 2 is less than 5.
• Therefore we round it down to 6.7.

	As shown on the number line, 6.72 is closer to 6.70 than to 6.80.

Rounding decimals

Question 2