Estimating

1
Estimating
Estimation is used to check your answer is
roughly right, or in the right ball park,
or you may go shopping and want to work out if
you have enough money to pay.
Look at this list of shopping and estimate how
much it will cost
Estimate to
2.00
Loaf of bread 1.70 Litre of milk 0.97 750g
packet of Cornflakes 2.43 Tin of baked
beans 0.42 Frozen chips 1.13 Fish
fingers 2.07 Chocolate dessert 3.87
1.00
2.50
0.50
1.00
2.00
4.00
Total
12.00
Note All estimates are to 1 significant figure 1
s.f.
2
Estimating
Estimate the value of
1 mark
1 mark
1 mark
x
60
100
6000
60
57.2 x 110 2.146 x 46.9


x
100
2
50
Round each value to 1.s.f
Calculate the exact value on your calculator
62.52 to 4 s.f.
In an exam question 3 marks would be awarded like
this
3
Estimating
Estimate the value of
x
20
60
1200
2400
23.4 x 62.7 0.43


0.5
0.5
Round each value to 1.s.f
Remember what divide means
Look at it and wonder how many piles of?
Similarly
20 0.1
200

4
Estimating
Sometimes you can round the numbers to make the
calculation easier
Estimate the value of
112.2 x 75.9 6.9 x 5.1
x
100
75
7000
200


35
7 x 5
5
Estimating
70
300
6
20
2
10
240
1.5