Rounding to a Given Place Value (Cambridge (CIE) IGCSE International Maths)

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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

  • 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, 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)

Worked Example

Round the following numbers to 2 decimal places.

(i) 345.254

(ii) 0.295 631

(iii) 4.998

(i) 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)

345.25 circle enclose 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 place

   

(ii) Identify the second decimal place (9)
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)

0.29 circle enclose 5 space 631 

As this digit is greater than or equal to 5 we will round the number up

0.30 (2 d.p.)

The zero is important to show we have rounded to two decimal places

  

(iii) 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)

4.99 circle enclose 8

As this digit is 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

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Naomi C

Author: Naomi C

Expertise: Maths

Naomi graduated from Durham University in 2007 with a Masters degree in Civil Engineering. She has taught Mathematics in the UK, Malaysia and Switzerland covering GCSE, IGCSE, A-Level and IB. She particularly enjoys applying Mathematics to real life and endeavours to bring creativity to the content she creates.

Dan Finlay

Author: Dan Finlay

Expertise: Maths Lead

Dan graduated from the University of Oxford with a First class degree in mathematics. As well as teaching maths for over 8 years, Dan has marked a range of exams for Edexcel, tutored students and taught A Level Accounting. Dan has a keen interest in statistics and probability and their real-life applications.