1.2.4

Rounding to Check Your Answer

Test yourself on Rounding to Check Your Answer

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Using Rounding to the Nearest 1,000 to Check Your Answers

You can use rounding to check if our answers are correct. You can use rounding to check your answers from written methods or mental maths.

Example

Example

  • I have worked out that 3,427 + 2,372 = 6,699 but I'm not very confident in my answer.
  • I can use rounding to check if my answer is roughly correct.
Round both numbers

Round both numbers

  • I can round both numbers to the nearest 10/100/1,000 to check.
    • 3,427 to the nearest thousand is 3,000.
    • 2,372 to the nearest thousand is 2,000.
Adding the rounded numbers

Adding the rounded numbers

  • I can add the rounded numbers together to make an estimate for the actual answer.
    • 3,000 + 2,000 = 5,000
    • As I am rounding to the nearest 1,000, my ‘real’ answer needs to be up to 1,000 away from my estimate if it is correct.
Is it less than 1,000 away?

Is it less than 1,000 away?

  • I originally said that 3,427 + 2,372 = 6,699.
  • 6,699 is more than 1,000 away from our estimated answer (5,000).
    • This means that 6,699 is NOT the correct answer and I should try again.

Using Rounding to the Nearest 100 to Check Your Answers

You can use rounding to check if our answers are correct. You can use rounding to check your answers from written methods or mental maths.

Example

Example

  • My friend tried to work out the answer to 3,427 + 2,372 to help me.
    • My friend thinks 3,427 + 2,372 = 5,799.
  • We need to use rounding to check the answer.
Round both numbers

Round both numbers

  • To get a more accurate estimate, I will round to the nearest 100 this time to work out my estimate.
    • 3,427 to the nearest hundred is 3,400.
    • 2,372 to the nearest hundred it would be 2,400.
Adding the rounded numbers

Adding the rounded numbers

  • I can add the rounded numbers together to make an estimate for the actual answer.
    • 3,400 + 2,400 = 5,800
    • As I am rounding to the nearest 100, my friend's ‘real’ answer needs to be up to 100 away from my estimate if it is correct.
Is it less than 100 away?

Is it less than 100 away?

  • My friend originally said that 3,427 + 2,372 = 5,799.
  • 5,799 is less than 100 away from our estimated answer (5,800).
    • This means that 5,799 could be the correct answer.
    • This doesn't mean it is definitely correct though.
Jump to other topics
1

Year 5 - Number

1.1

Number & Place Value

1.1.1The Value of Digits to Millions1.1.2Smallest & Biggest Numbers to Millions1.1.3Ordering Numbers to Millions1.1.4Counting in Powers of 101.1.5Counting in Negative Numbers1.1.6Rounding Numbers up to 1,000,0001.1.7Reading Roman Numerals
1.2

Addition & Subtraction

1.2.1Written Methods for Adding Large Numbers1.2.2Written Methods for Subtracting Large Numbers1.2.3Mental Addition & Subtraction1.2.4Rounding to Check Your Answer
1.3

Multiplication & Division

1.3.1Multiples1.3.2Factors1.3.3Prime Numbers1.3.4Prime Factors1.3.5Composite Numbers1.3.6Factor Trees1.3.7Multiplication by a 1 Digit Number1.3.8Long Multiplication Using Column Method1.3.9Times Tables1.3.10Division1.3.11Multiplying & Dividing by 10, 100 & 1,0001.3.12Square & Cube Numbers
1.4

Fractions & Decimals

1.4.1Compare & Order Fractions1.4.2Identifying Equivalent Fractions1.4.3Add & Subtract Fractions1.4.4Mixed Numbers & Improper Fractions1.4.5Multiplying Fractions by Whole Numbers1.4.6Converting Between Decimals & Fractions1.4.7Rounding Decimals1.4.8Ordering Decimals
2

Year 5 - Measurement

2.1

Measures

2.1.1Metric Measurements2.1.2Imperial Measurements
2.2

Perimeter & Area

2.2.1Perimeter2.2.2Area
2.3

Time

2.3.1Units of Time
3

Year 5 - Geometry

3.1

Properties of 3D Shapes

3.1.1Types of 3D Shapes3.1.2Faces, Edges & Vertices
3.2

Properties of 2D Shapes

3.2.1Polygons
3.3

Angles

3.3.1Angles in Degrees3.3.2Types of Angle3.3.3Finding Missing Angles
3.4

Position & Direction

3.4.1Reflection & Translation
4

Year 5 - Statistics

4.1

Graphs

4.1.1Line Graphs4.1.2Tables4.1.3Timetables
5

Year 6 - Number

5.1

Number & Place Value

5.1.1The Value of Digits to Ten Millions5.1.2Ordering Numbers to Millions5.1.3Rounding5.1.4Negative Numbers
5.2

Multiplication & Division

5.2.1Multiplication by a 2 Digit Number5.2.2Division5.2.3Multiples5.2.4Factors5.2.5Primes
5.3

Mental Maths

5.3.1Multiplying & Dividing by 10, 100 & 1,0005.3.2Addition & Subtraction5.3.3Adding & Subtracting 10, 100 & 1,0005.3.4Multiplication & Division
5.4

Order of Operations

5.4.1BIDMAS
5.5

Problem Solving

5.5.1Addition & Subtraction Multi-step Problems5.5.2Problem Solving with Proportion
5.6

Fractions & Decimals

5.6.1Simplifying Fractions Using Equivalents5.6.2Ordering Different Types of Fraction5.6.3Adding & Subtracting Fractions5.6.4Adding & Subtracting Mixed Numbers5.6.5Multiplying Fractions5.6.6Dividing Fractions by Whole Numbers5.6.7Converting Between Decimals & Fractions5.6.8Dividing Decimals
6

Year 6 - Ratio & Proportion

6.1

Ratio

6.1.1Using Ratios6.1.2Simplifying Ratios
6.2

Percentages

6.2.1Calculating Percentages
6.3

Scale

6.3.1Scale of 2D Shapes
7

Year 6 - Algebra

7.1

Sequences

7.1.1Describing Sequences7.1.2Finding Gaps in Sequences
7.2

Missing Number Problems

7.2.1Missing Number Problems
7.3

Equations

7.3.1Balancing Equations7.3.2Combining Two Variables
8

Year 6 - Measurement

8.1

Problem Solving

8.1.1Problem Solving with Measures
8.2

Unit Conversion

8.2.1Conversion Between Miles & Kilometres
8.3

Perimeter, Area & Volume

8.3.1Area8.3.2Volume8.3.3Nets8.3.4Faces, Edges & Vertices
8.4

Angles

8.4.1Types of Angle8.4.2Finding Missing Angles8.4.3Finding Missing Angles in Triangles8.4.4Vertically Opposite Angles
8.5

Circles

8.5.1Parts of a Circle
8.6

Coordinate Grids

8.6.1Positions on Coordinate Grids8.6.2Reflection & Translation
9

Year 6 - Statistics

9.1

Displaying Data

9.1.1Pie Charts9.1.2Line Graphs
9.2

Averages

9.2.1Mean

Practice questions on Rounding to Check Your Answer

Can you answer these? Test yourself with free interactive practice on Seneca — used by over 10 million students.

  1. 1
    Which of these would be a reasonable estimate for 2,947 + 6,284?Multiple choice
  2. 2
    Which of these would be a reasonable estimate for 3,832 + 1,295?Multiple choice
  3. 3
    Which of these would be a reasonable estimate for 1,145 + 2,814?Multiple choice
  4. 4
    Which of these calculations will give the most accurate estimate for 3,872 + 7,230?Multiple choice
  5. 5
    Which of these calculations will give the most accurate estimate for 1,512 + 3,327?Multiple choice
Answer all questions on Rounding to Check Your Answer

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Mental Addition & Subtraction

Multiples