5.2.3

Estimation & Inverse Operations

Test yourself on Estimation & Inverse Operations

Test your knowledge with free interactive questions on Seneca — used by over 10 million students.

Checking Answers with Estimation and Inverse Operations

We can use estimation and inverse operations to check our answers are correct.

Example

Example

Let’s use the same calculation for both estimating and inverse.
5,463 + 2,943 = ?

Estimation

Estimation

To estimate the answer, we use rounding to help us:
- 5,463 $\rightarrow$ 5,500
- 2,943 $\rightarrow$ 3,000
5,500 + 3,000 = 8,500
This means we should expect our answer to be around 8,500.

Addition and subtraction

Addition and subtraction

Let's say we get the answer:
- 5,463 + 2,943 = 8,306
Let's use the inverse to check:
- 8,306 - 2,943 = 5,363
We should have gotten 5,463, so this means our answer is NOT correct.
The answer is actually 8,406.

1

Year 3 - Number

2

Year 3 - Measurement

2.1

Length

2.1.1Length 2.1.2Comparing Lengths 2.1.3Add & Subtract Lengths 2.1.4Perimeter

2.2

Mass

2.2.1Mass 2.2.2Comparing Masses 2.2.3Add & Subtract Masses

2.3

Volume & Capacity

2.3.1Volume & Capacity 2.3.2Comparing Volumes 2.3.3Add & Subtract Volumes

2.4

Money

2.4.1Money 2.4.2Counting Money 2.4.3Adding & Subtracting Money

2.5

Time

2.5.1Units of Time 2.5.2Clocks 2.5.3Telling the Time 2.5.4Time of the Day 2.5.512-Hour & 24-Hour Clocks 2.5.6Measuring Time

3

Year 3 - Geometry

3.1

Angles

3.1.1Angles in Degrees 3.1.2Types of Angle

3.2

Properties of Shapes

3.2.12D Shapes 3.2.23D Shapes

3.3

Straight Lines

3.3.1Straight Lines 3.3.2Parallel & Perpendicular Lines

4

Year 3 - Statistics

4.1

Statistics

4.1.1Statistics 4.1.2Pictograms & Bar Charts

5

Year 4 - Number

6

Year 4 - Measurement

6.1

Units

6.1.1Metric Measurements 6.1.2Adding & Subtracting Money

6.2

Time

6.2.1Converting Units of Time 6.2.2Changing the 12-Hour Clock to the 24-Hour Clock 6.2.3Changing the 24-hour Clock to the 12-Hour Clock

7

Year 4 - Geometry

7.1

Properties of Shapes

7.1.1Symmetry 7.1.2Types of Triangle 7.1.3Quadrilaterals

7.2

Perimeter & Area

7.2.1Perimeter 7.2.2Area

7.3

Position & Direction

7.3.1Coordinates 7.3.2Translation

8

Year 4 - Statistics

8.1

Statistics

8.1.1Types of Data 8.1.2Pictograms & Bar Charts 8.1.3Line Graphs

Jump to other topics

1

Year 3 - Number

2

Year 3 - Measurement

2.1

Length

2.1.1Length 2.1.2Comparing Lengths 2.1.3Add & Subtract Lengths 2.1.4Perimeter

2.2

Mass

2.2.1Mass 2.2.2Comparing Masses 2.2.3Add & Subtract Masses

2.3

Volume & Capacity

2.3.1Volume & Capacity 2.3.2Comparing Volumes 2.3.3Add & Subtract Volumes

2.4

Money

2.4.1Money 2.4.2Counting Money 2.4.3Adding & Subtracting Money

2.5

Time

2.5.1Units of Time 2.5.2Clocks 2.5.3Telling the Time 2.5.4Time of the Day 2.5.512-Hour & 24-Hour Clocks 2.5.6Measuring Time

3

Year 3 - Geometry

3.1

Angles

3.1.1Angles in Degrees 3.1.2Types of Angle

3.2

Properties of Shapes

3.2.12D Shapes 3.2.23D Shapes

3.3

Straight Lines

3.3.1Straight Lines 3.3.2Parallel & Perpendicular Lines

4

Year 3 - Statistics

4.1

Statistics

4.1.1Statistics 4.1.2Pictograms & Bar Charts

5

Year 4 - Number

6

Year 4 - Measurement

6.1

Units

6.1.1Metric Measurements 6.1.2Adding & Subtracting Money

6.2

Time

6.2.1Converting Units of Time 6.2.2Changing the 12-Hour Clock to the 24-Hour Clock 6.2.3Changing the 24-hour Clock to the 12-Hour Clock

7

Year 4 - Geometry

7.1

Properties of Shapes

7.1.1Symmetry 7.1.2Types of Triangle 7.1.3Quadrilaterals

7.2

Perimeter & Area

7.2.1Perimeter 7.2.2Area

7.3

Position & Direction

7.3.1Coordinates 7.3.2Translation

8

Year 4 - Statistics

8.1

Statistics

8.1.1Types of Data 8.1.2Pictograms & Bar Charts 8.1.3Line Graphs

Unlock your full potential with Seneca Premium

Unlimited access to 10,000+ open-ended exam questions
Mini-mock exams based on your study history
Unlock 800+ premium courses & e-books

Get started with Seneca Premium

Written Methods for Subtracting Large Numbers

Solving Two-Step Problems