Rounding to Check Your Answer

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

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

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

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?

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

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

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

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?

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.

1Year 5 - Number

1.1Number & Place Value

1.1.1The Value of Digits to Millions

1.1.2Smallest & Biggest Numbers to Millions

1.1.3Ordering Numbers to Millions

1.1.4Counting in Powers of 10

1.1.5Counting in Negative Numbers

1.1.6Rounding Numbers up to 1,000,000

1.1.7Reading Roman Numerals

1.2Addition & Subtraction

1.2.1Written Methods for Adding Large Numbers

1.2.2Written Methods for Subtracting Large Numbers

1.2.3Mental Addition & Subtraction

1.2.4Rounding to Check Your Answer

1.3Multiplication & Division

1.3.1Multiples

1.3.2Factors

1.3.3Prime Numbers

1.3.4Prime Factors

1.3.5Composite Numbers

1.3.6Factor Trees

1.3.7Multiplication by a 1 Digit Number

1.3.8Long Multiplication Using Column Method

1.3.9Times Tables

1.3.10Division

1.3.11Multiplying & Dividing by 10, 100 & 1,000

1.3.12Square & Cube Numbers

1.4Fractions & Decimals

1.4.1Compare & Order Fractions

1.4.2Identifying Equivalent Fractions

1.4.3Add & Subtract Fractions

1.4.4Mixed Numbers & Improper Fractions

1.4.5Multiplying Fractions by Whole Numbers

1.4.6Converting Between Decimals & Fractions

1.4.7Rounding Decimals

1.4.8Ordering Decimals

2Year 5 - Measurement

2.1Measures

2.1.1Metric Measurements

2.1.2Imperial Measurements

2.2Perimeter & Area

2.2.1Perimeter

2.2.2Area

2.3Time

2.3.1Units of Time

3Year 5 - Geometry

3.1Properties of 3D Shapes

3.1.1Types of 3D Shapes

3.1.2Faces, Edges & Vertices

3.2Properties of 2D Shapes

3.2.1Polygons

3.3Angles

3.3.1Angles in Degrees

3.3.2Types of Angle

3.3.3Finding Missing Angles

3.4Position & Direction

3.4.1Reflection & Translation

4Year 5 - Statistics

4.1Graphs

4.1.1Line Graphs

4.1.2Tables

4.1.3Timetables

5Year 6 - Number

5.1Number & Place Value

5.1.1The Value of Digits to Ten Millions

5.1.2Ordering Numbers to Millions

5.1.3Rounding

5.1.4Negative Numbers

5.2Multiplication & Division

5.2.1Multiplication by a 2 Digit Number

5.2.2Division

5.2.3Multiples

5.2.4Factors

5.2.5Primes

5.3Mental Maths

5.3.1Multiplying & Dividing by 10, 100 & 1,000

5.3.2Addition & Subtraction

5.3.3Adding & Subtracting 10, 100 & 1,000

5.3.4Multiplication & Division

5.4Order of Operations

5.4.1BIDMAS

5.5Problem Solving

5.5.1Addition & Subtraction Multi-step Problems

5.5.2Problem Solving with Proportion

5.6Fractions & Decimals

5.6.1Simplifying Fractions Using Equivalents

5.6.2Ordering Different Types of Fraction

5.6.3Adding & Subtracting Fractions

5.6.4Adding & Subtracting Mixed Numbers

5.6.5Multiplying Fractions

5.6.6Dividing Fractions by Whole Numbers

5.6.7Converting Between Decimals & Fractions

5.6.8Dividing Decimals

6Year 6 - Ratio & Proportion

6.1Ratio

6.1.1Using Ratios

6.1.2Simplifying Ratios

6.2Percentages

6.2.1Calculating Percentages

6.3Scale

6.3.1Scale of 2D Shapes

7Year 6 - Algebra

7.1Sequences

7.1.1Describing Sequences

7.1.2Finding Gaps in Sequences

7.2Missing Number Problems

7.2.1Missing Number Problems

7.3Equations

7.3.1Balancing Equations

7.3.2Combining Two Variables

8Year 6 - Measurement

8.1Problem Solving

8.1.1Problem Solving with Measures

8.2Unit Conversion

8.2.1Conversion Between Miles & Kilometres

8.3Perimeter, Area & Volume

8.3.1Area

8.3.2Volume

8.3.3Nets

8.3.4Faces, Edges & Vertices

8.4Angles

8.4.1Types of Angle

8.4.2Finding Missing Angles

8.4.3Finding Missing Angles in Triangles

8.4.4Vertically Opposite Angles

8.5Circles

8.5.1Parts of a Circle

8.6Coordinate Grids

8.6.1Positions on Coordinate Grids

8.6.2Reflection & Translation

9Year 6 - Statistics

9.1Displaying Data

9.1.1Pie Charts

9.1.2Line Graphs

9.2Averages

9.2.1Mean

Jump to other topics