Rounding to a Given Place Value
How do I round a number to a given place value?
- Identify the digit in the required place value
- Identify the two options that the number could round to
- Count in the units you are rounding to, find the first value below and the next value above the number you are rounding
- E.g. Round 1294 to the nearest 100, count in 100's, the number will round down to 1200 or up to 1300
- Be careful if your digit is a 9 and the next number up will affect the higher place values
- E.g. Rounding 1798 to the nearest 10, count in 10's, the number will round down to 1790 or up to 1800
- Count in the units you are rounding to, find the first value below and the next value above the number you are rounding
- Circle the number to the right of the required place value
- If the circled number is 5 or more then you round to the bigger number
- If the circled number is less than 5 then you round to the smaller number
- Put a zero in any following place values before the decimal point
- E.g. 1567.45 to the nearest 100 would be 1600
How do I round a number to a given decimal place?
- Identify the position of the decimal place you are rounding to
- Identify the two options that the number could round to
- E.g. Round 7.82741 to 3 d.p., count in 0.001's, the number will round down to 7.827 or up to 7.828
- Circle the number to the right of the required decimal place
- If the circled number is 5 or more then you round to the bigger number
- If the circled number is less than 5 then you round to the smaller number
- E.g. 2.435123 to the nearest 2 d.p. would be 2.44
- When rounding to decimal places make sure you leave your answer with the required amount of decimal places
- Do not put any zeros after the position of the decimal place you are rounding to
- E.g. 1267 to the nearest 100 is 1300 but 1.267 to two decimal places (nearest 100th) is 1.27 not 1.270
- If asked for a certain number of decimal places then you must give an answer with that number of decimal places
- E.g. 2.395 to two decimal places is 2.40 do not write 2.4
- Do not put any zeros after the position of the decimal place you are rounding to
- In money calculations, unless the required degree of accuracy is stated in the question
- Leave your answer in a whole number of dollars, pounds, etc. if it seems sensible
- Or round to 2 decimal places
What is truncation?
- Truncation is essentially the same as rounding down to a given degree of accuracy
- It is usually used in situations where a whole number of items is needed
- E.g. If the answer to a question about the maximum number of people that can fit in a taxi is 4.6
- Truncate the answer to 4, rather than round to 5
- E.g. If the answer to a question about the maximum number of people that can fit in a taxi is 4.6
Worked example
Round the following numbers to 2 decimal places.
345.254
0.295 631
4.998
Identify the second decimal place (5)
Count in 0.01's, identify the first number below (345.25) and the next number above (345.26)
Circle the digit to the right of the second decimal place (4)
As this digit is less than 5 we will round the number down
345.25 (2 d.p.)
No zeros are required after the second decimal places
Count in 0.01's, identify the first number below (0.29) and the next number above (0.30)
Circle the digit to the right of the second decimal place (5)
0.30 (2 d.p.)
The zero is important to show we have rounded to two decimal places
Identify the second decimal place (9)
Count in 0.01's, identify the first number below (4.99) and the next number above (5.00)
Circle the digit to the right of the second decimal place (8)
As this digit greater than or equal to 5 we will round the number up
5.00 (2 d.p.)
Two zeros are needed to show we have rounded to 2 decimal places