New
New
Year 8

Estimating numerical calculations

I can estimate numerical calculations.

New
New
Year 8

Estimating numerical calculations

I can estimate numerical calculations.

warning

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

Switch to our new teaching resources now - designed by teachers and leading subject experts, and tested in classrooms.

Lesson details

Key learning points

  1. All numbers can be rounded to a given number of significant figures.
  2. Estimating gives you an idea of the size of an answer in context.
  3. To estimate an answer you will often round to one significant figure.
  4. Sometimes it makes sense to round to a different degree of accuracy when making an estimate.

Keywords

  • Estimate - A quick estimate for a calculation is obtained from using approximate values, often rounded to 1 significant figure.

  • Significant figures - Significant figures are the digits in a number that contribute to the accuracy of the number.

Common misconception

Division by 0.5 is the same as doubling.

Reiterate the division of a number is the same as the multiplication of the reciprocal e.g The division of 0.5 is the same as multiplying by 2. e.g The division of 0.1 is the same as multiplying by 10.

It is important pupils have a real life reference of length. E.g Measure how wide their hand is. Use this to estimate how wide the table is. E.g Measure how wide their fingernail is. Use this to estimate how long a pencil sharpener is.
Teacher tip

Licence

This content is © Oak National Academy Limited (2024), licensed on Open Government Licence version 3.0 except where otherwise stated. See Oak's terms & conditions (Collection 2).

Lesson video

Loading...

6 Questions

Q1.
___________ figures are the digits in a number that contribute to the accuracy of the number. The first __________ figure is the first non-zero digit.
Imperative
Important
Correct answer: Significant
Super important
Vital
Q2.
5689 rounded to 1 s.f. is .
Correct Answer: 6000, six thousand
Q3.
428.62 rounded to 1 s.f. is .
Correct Answer: 400, four hundred
Q4.
428.62 rounded to 2 s.f. is .
Correct Answer: 430, four hundred and thirty
Q5.
Sam correctly rounds an integer to the nearest 10. Sam's answer is 80. What could Sam's unrounded integer be?
Correct answer: 78
91
94
Correct answer: 75
Correct answer: 84
Q6.
Laura correctly rounds a number to 1 significant figure. Her answer is 8. What could Laura's unrounded number be?
Correct answer: 8.457
8.547
Correct answer: 7.849
Correct answer: 7.584
7.458

6 Questions

Q1.
A quick for a calculation is obtained from using approximate values, often rounded to 1 significant figure.
guess
number
guess-timate
Correct answer: estimate
round
Q2.
Which of the following is the most accurate estimate calculation for 856 × 465?
Correct answer: 900 × 500
1000 × 500
500 × 500
1000 × 1000
Q3.
Which of the following are good, quick estimate calculations for 578 ÷ 1.785?
Correct answer: 600 ÷ 2
Correct answer: 580 ÷ 2
600 ÷ 1.8
578 ÷ 1.8
Q4.
Which of the following are good, quick estimate calculations for $${4.56\times8.95} \over {7.65}$$?
Correct answer: $${5\times10} \over {10}$$
Correct answer: $${5\times10} \over {8}$$
Correct answer: $${5\times8} \over {8}$$
$${4.5\times9} \over {7.7}$$
Q5.
Which of the following are correct estimates for $${18.96\times2.15} \over {0.546}$$?
$${20\times2} \over {0.5}$$ $$ = 20$$
Correct answer: $${20\times2} \over {0.5}$$ $$ = 80$$
$${19\times2} \over {0.5}$$ $$ = 19$$
Correct answer: $${19\times2} \over {0.5}$$ $$= 76$$
Q6.
Given Alex is of average secondary school pupil height. An estimate of the height of the elephant is m. Give your answer to 1 decimal place.
An image in a quiz
Correct Answer: 3.0, 3.1, 3.2, 2.9, 2.8