Estimation
Finding an approximate answer quickly to check reasonableness.
Key idea
Finding an approximate answer quickly to check reasonableness.
In depth
Estimating gives a quick, approximate answer to check whether an exact answer is sensible. Round numbers to friendly values first, then compute. It catches big mistakes like misplaced decimal points.
Worked example
Estimate 398 × 21: about 400 × 20 = 8,000. The exact answer 8,358 is close, so it is plausible.
Real-world uses
- Checking a restaurant bill before paying
- Judging how much paint or fabric a room needs
Common mistake
Rounding in a way that hides the answer, such as rounding everything down when the error should balance.
How to learn this
- Read the key idea and say it in your own words.
- Work through the worked example, then try a similar problem.
- Use the interactive lesson’s visual and mini-quiz to check the pattern.
Frequently asked questions
What is Estimation?
Finding an approximate answer quickly to check reasonableness. It is a topic at the beginner level in Arithmetic & Number Sense.
Where is Estimation used in real life?
Real-world examples: Checking a restaurant bill before paying; Judging how much paint or fabric a room needs.
What should I learn before Estimation?
Make sure you are comfortable with Rounding, the previous topic in Arithmetic & Number Sense.
What is a common mistake with Estimation?
Rounding in a way that hides the answer, such as rounding everything down when the error should balance.
How can I practise Estimation?
Open the interactive lesson, play with the visual, then answer the three-question mini-quiz. Getting two right marks the topic complete.
What comes after Estimation?
Move on to Mental Math Strategies next.
Related beginner topics in Arithmetic & Number Sense
- Counting & Cardinality – Assigning one number word to each object to find how many there are.
- Place Value – The value of a digit depends on its position: ones, tens, hundreds and so on.
- Number Line – A line where numbers are placed in order at equal spacing to compare and add them.
- Comparing Numbers – Use <, > and = to say which number is smaller, larger or equal.
- Ordering Numbers – Arranging numbers from least to greatest or the reverse.
- Even and Odd Numbers – Even numbers divide by 2 with no remainder; odd numbers leave remainder 1.