Checking by estimating | Maths | Quizalize & Oak National Academy

Starter quiz

Significant figures are the digits in a number that contribute to the accuracy of the number. The first significant figure is the first __________ digit.

digit between 5 and 9

important

non-zero ✓

zero
Which of the following are good estimate calculations for 989 × 213.4?

1000 × 200 ✓

1000 × 210 ✓

1000 × 213 ✓

9 × 2
Which of the following are good, quick estimate calculations for 432.4 ÷ 1.85?

400 ÷ 2 ✓

400 ÷ 1.85

500 ÷ 2 ✓

5 ÷ 2
Which of the following are correct estimates for ${17.9}\over {0.532}$ ?

${18}\over {0.5}$ $= 9$

${20}\over {0.5}$ $= 10$

${18}\over {0.5}$ $= 36$ ✓

${20}\over {0.5}$ $= 40$ ✓
Which of the following is the correct estimate for ${3.4\times3.92}\over {0.511}$ ?

${3\times4}\over {0.5}$ $= 12$

${3\times4}\over {0.5}$ $= 24$ ✓

${3\times4}\over {0.5}$ $= 6$

${3.4\times3.92}\over {0.511}$ $= 26.082$
Horses and ponies are measured using ‘hands’ as a unit, where the width of the hand is used. This pony has a height of 9 hands. Estimate the height of the pony.

200 cm

150 cm

90 cm ✓

50 cm

10 cm

Match the following numbers to the correct rounded value.

9212

⇔

9000 (1 s.f.) ✓

8934.89

⇔

8934.9 (1 d.p.) ✓

8910

⇔

8900 (2 s.f.) ✓

8934.894

⇔

8934.89 (2 d.p.) ✓
Which of the following are sensible measurements for the lengths of an average house?

Front: 844 mm , Side: 596 mm

Front: 0.844 km, Side: 0.896 km

Front: 844 cm, Side: 596 cm ✓

Front: 8.44 m, Side: 5.96 m ✓
A bookshop wants to buy the new sci-fi books to sell in their store. The bookshop has £789 and each book costs £18.99. Select the correct estimate for the number of books the bookshop can buy.

${800} \over {20}$ = 4 books

${800} \over {20}$ = 40 books ✓

${800} \over {18.99}$ = 42.127 books

${800} \over {20}$ = 4000 books
Select the approximate answer to $\frac{8}{15}\times\ 9$ .

3

5 ✓

7

12

15
A bicycle costs £18.99 for 1 week's hire. Which of the following shows the estimate to hire 6 bicycles for 4 weeks?

£20 × 6 × 4 = £240

£20 × 6 × 4 = £480 ✓

£20 × 6 × 4 = £2400

£20 × 6 × 4 = £4800

£20 × 6 × 4 = £24 000
Jun buys paper £3.25, USB £ $\square$ , stamps £4.95, crisps £0.85, staples £2.30 and plug £1.99. He pays with a £20 note and receives about £2 back in change. Estimate the cost of the USB.

£1

£2

£3

£5 ✓

£7

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Estimation should give you an idea of the size of an answer.
It is useful to estimate the answer to calculations so you can check your answers make sense.
Errors in calculations can be found by using estimates.

When rounding a number, pupils write the first significant digit(s). e.g 36 789 is 4.

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

Significant figures - Significant figures are the digits in a number that contribute to the accuracy of the number.
Estimate - A quick estimate for a calculation is obtained from using approximate values, often rounded to 1 significant figure.