Hints and tips The symbol ≈ means ‘approximately equal to’.
Example 4
The approximation for the division 89.1 ÷ 2.98, is 90 ÷ 3 = 30. Find an approximate answer to 24.3 ÷ 3.87. Round each number in the calculation to 1 sf. 24.3 ÷ 3.87 ≈ 20 ÷ 4 = 5 So 24.3 ÷ 3.87 ≈ 5.
A quick approximation will help prevent you from giving an answer that is much too big or too small.
Exercise 6D 1
Work out approximate answers to these calculations.
a 5435 × 7.31
b 5280 × 3.211
c 63.24 × 3.514 × 4.2
d 3508 × 2.79
e 72.1 × 3.225 × 5.23
f 470 × 7.85 × 0.99
g 354 ÷ 79.8
h 36.8 ÷ 1.876
i 5974 ÷ 5.29
Use a calculator to see how close your approximations are to the actual answers.
2
3
Work out the approximate monthly pay for each annual salary given.
a £35 200
b £25 600
c £18 125
d £8420
Work out each person’s approximate annual pay.
a Kevin who earns £270 a week b Malcolm who earns £1528 a month c David who earns £347 a week MR
4
A farmer bought 2713 kg of seed at a cost of £7.34 per kilogram. Estimate the total cost of this seed.
5
By rounding, work out an approximate answer to each calculation.
6
a
573 + 783 107
b
783 − 572 24
c
352 + 657 999
d
1123 − 689 354
e
589 + 773 658 − 351
f
793 − 569 998 − 667
g
354 + 656 997 − 656
h
1124 − 661 355 + 570
i
28.3 × 19.5 97.4
j
78.3 × 22.6 3.69
k
3.52 × 7.95 15.9
l
11.78 × 77.8 39.4
Work out an approximate answer for each calculation.
a 208 ÷ 0.378
b 96 ÷ 0.48
c 53.9 ÷ 0.58
d 14.74 ÷ 0.285
e 28.7 ÷ 0.621
f 406.9 ÷ 0.783
Use a calculator to see how close your approximations are to the actual answers.
7
A litre of paint will cover an area of about 8.7 square metres (m2). Approximately how many 1-litre cans will I need to paint a room with a total surface area of 73 m2? 6.3 Approximating calculations
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