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Key learning points

When estimating ages, it is convention to use truncation.
Truncation can be used to estimate any integer to a given accuracy.
Truncation can be used to estimate any number to a given accuracy.

Keywords

Truncate - Truncation is the simplifying a number by 'cutting off' one or more of the digits and replacing them with zeros if necessary to preserve place value.
A degree of accuracy - A degree of accuracy shows how precise a number or measurement is.

Common misconception

When truncating, pupils are tempted to round. Also, when truncating, they cut off the number without thinking about the magnitude.

The use of the place value table shows the magnitude of the number, thus preserving their place value when truncating.

To help you plan your year 8 maths lesson on: Truncating, download all teaching resources for free and adapt to suit your pupils' needs...

We use truncating a lot in real life, ask the pupils in class to write down the real life examples of when they have truncated, when they have rounded and when have they needed to use the exact values. This activity allows pupils to appreciate the importance or each and their differences.

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This content is © Oak National Academy Limited (2025), licensed on Open Government Licence version 3.0 except where otherwise stated. See Oak's terms & conditions (Collection 2).

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Starter quiz

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6 Questions

Q1.

__________ shows how precise a number or measurement is.

Correct answer: An approximation

A degree of accuracy

A guess

A guess-stimate

Rounding

Q2.

Match each number to its rounded value.

Correct Answer:323,320 (2 s.f.)

320 (2 s.f.)

Correct Answer:294.82,294.8 (1 d.p.)

294.8 (1 d.p.)

Correct Answer:291,290 (2 s.f.)

290 (2 s.f.)

Correct Answer:294.829,294.83 (2 d.p.)

294.83 (2 d.p.)

Q3.

A square plot of grass has a length of 2.89 m to 2 decimal places. Select the correct estimate for the area of the square grass plot.

Correct answer: 3 × 3 = 9 m²

3 × 3 = 6 m²

3 + 3 + 3 + 3 = 12 m²

3 + 3 + 3 + 3 = 12 m

Q4.

Match each number to its rounded value.

Correct Answer:0.0038903,0.0039 (2 s.f.)

0.0039 (2 s.f.)

Correct Answer:0.038903,0.04 (2 d.p.)

0.04 (2 d.p.)

Correct Answer:0.00038903,0.0004 (1 s.f.)

0.0004 (1 s.f.)

Correct Answer:0.000038903,0.000039 (2 s.f.)

0.000039 (2 s.f.)

Q5.

Which of the following are correct, quick estimate calculations for

\frac{4.56 \times 8.95}{0.498}

?

Correct answer:

\frac{5 \times 9}{0.5}

= 90

\frac{5 \times 10}{0.5}

= 25

\frac{5 \times 9}{0.5}

= 22.5

Correct answer:

\frac{5 \times 10}{0.5}

= 100

Q6.

Match each calculation to its correct approximate answer.

Correct Answer:

\frac{19.89}{0.498}

,

\approx 40

$\approx 40$

Correct Answer:

\frac{19.89}{0.2134}

,

\approx 100

$\approx 100$

Correct Answer:

\frac{19.89}{0.1111}

,

\approx 200

$\approx 200$

Correct Answer:

\frac{19.89}{2.073}

,

\approx 10

$\approx 10$

Exit quiz

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6 Questions

Q1.

__________ is the simplifying a number by 'cutting off' one or more of the digits and replacing them with zeros if necessary to preserve place value.

Estimation

Guessing

Rounding

Correct answer: Truncation

Q2.

Match each number with its truncated value to 1 significant figure.

Correct Answer:46 347 823,40 000 000

40 000 000

Correct Answer:4634,4000

4000

Correct Answer:46.347,40

40

Correct Answer:46 347.823,40 000

40 000

Correct Answer:4.634823,4

4

Q3.

Truncate 49.999999 to 3 significant figures. Select the correct response.

Jun says, "The answer is 50.0".

Andeep says, "The answer is 50.000".

Correct answer: Laura says, "The answer is 49.9".

Aisha says, "The answer is 50".

Q4.

Jacob thinks of a number. Truncated to 1 s.f. Jun's number is 100. Jun's number is a multiple of 8 and it is 105 when rounded to the nearest 5.

Correct Answer: 104

Q5.

Match the appropriate treatment of the answer (exact, rounded to truncated) to each context.

Correct Answer:Exact answer is required,A length of wood 37 m needs to be cut into 5 equal strips.

A length of wood 37 m needs to be cut into 5 equal strips.

Correct Answer:Rounded answer is required,A meal is £37 and you share it between 5 people and want to give a tip

A meal is £37 and you share it between 5 people and want to give a tip

Correct Answer:Truncated answer is required,You have £37 and want to buy as many £5 puzzle cubes as possible.

You have £37 and want to buy as many £5 puzzle cubes as possible.

Q6.

In computer science, ‘INT’ or ‘int’ is used to truncate a number so to only give the integers. For example, INT(56/10) has an output of 5. Match each computer instruction to its output.

Correct Answer:INT(78/8),9

9

Correct Answer:INT(90/8),11

11

Correct Answer:INT(123/10) + INT(7.9/3),14

14

Correct Answer:INT(789/10) + INT(56/3),96

96

Correct Answer:INT(1.65/10) + INT(76.6/3),25

25

Correct Answer:INT(8/0.5) + INT(12.65/2) − INT(9.8/6),21

21

Truncating

Truncating

These resources will be removed by end of Summer Term 2025.

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Lesson details

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Common misconception

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6 Questions

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6 Questions