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# Estimating Calculations

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by

## Mr Mattock

on 4 April 2017

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#### Transcript of Estimating Calculations

Estimating Calculations
Main Activity 1
Complete the RAG worksheet.
Starter
Estimation
Estimate the vlaue of these calculations:

(a) 8.73 x 17.3
38.4 + 23.6

(b) 150
4

(c) The cost of a electricity every month if the average annual bill is £1098.
L.O. Estimate calculations by rounding

Estimation
Estimate the vlaue of these calculations:

(a) 8.73 x 17.3
9 x 20 180
38.4 + 23.6
40+20 60

(b) 150
12
4
4

(c) The cost of a electricity every month if the average annual bill is £1098.

£1000/10 = £100
= = = 3
= = 3
Estimation
Are these estimates likely to be over-estimates or under estimates?

(a) 8.73 x 17.3
9 x 20 180
38.4 + 23.6
40+20 60

(b) 150
12
4
4

(c) The cost of a electricity every month if the average annual bill is £1098.

£1000/10 = £100
= = = 3
= = 3
Estimation
Are these estimates likely to be over-estimates or under estimates?

(a) 8.73 x 17.3
9 x 20 180
38.4 + 23.6
40+20 60

(b) 150
12
4
4

(c) The cost of a electricity every month if the average annual bill is £1098.

£1000/10 = £100
= = = 3
= = 3
Over-estimate, because the numerator is really less than 180 and the denominator really more than 60
Over-estimate, the numerator is really bigger than 12.
Over-estimate, as 12 x 100 = £1200 which is more
than the annual bill.
Starter
(a) 490 (needs a place holder) (b) 6020 (rounded down not up)
(c) 0.350 (needs an accuracy 0)
(d) 0.3 (rounded to 0.35 first, which led to 0.4)
(e) 40100 (needs 2 place holders)
Main Activity 2
State and justify which are over-estimates, which are under-estimates.
Are there any you can't be certain of?
Red: (a) 20 x 50 = 1000 (b) 90/20 = 4.5 (c) 80/16 = 5
(d) 36/0.3 = 120 (e) 80/20 = 4
Estimating calculations
Typically to estimate a calculation, each number in the calculation is rounded to 1.s.f, unless it is easier
to round to a different accuracy.

When estimating square roots, we typically round
to the nearest square number.
Amber: (a) 6 x 10 = £60 (b) 200/50 = 4 hours
(c) £1.20 + £4.00 + £1.00 = £6.20
(d) 200/2 = 100 mph
Green: (a) 10 hours a week x 50 = 500 hours
(b) 500/20 = 25 days
(a) 3 x 3 = 9 (b) 3 x 16 = 48 (c) 2 x 3 x 7 = 42
(d) 4 + 9 ~ 16 = 4 (e) 49 - 16 ~ 36 = 6
(f) 1 + 36 ~ 36 = 6
Dice of Ultimate Power

1) Give a key word for the lesson.
2) Summarise one key point for the
lesson.
3) Explain one thing you have learned this
lesson.
4) State one thing you still don't understand following this lesson.
5) Suggest one thing you would like to find out
based on this lesson.
6) Free choice from 1 to 5, or another you make
up.
Red: (a) 20 x 50 = 1000 (b) 90/20 = 4.5 (c) 80/16 = 5 (d) 36/0.3 = 120 (e) 80/20 = 4
Amber: (a) 6 x 10 = £60 (b) 200/50 = 4 hours (c) £1.20 + £4.00 + £1.00 = £6.20 (d) 200/2 = 100 mph
Green: (a) 10 hours a week x 50 = 500 hours
(b) 500/20 = 25 days
(a) 3 x 3 = 9 (b) 3 x 16 = 48 (c) 2 x 3 x 7 = 42
(d) 4 + 9 ~ 16 = 4 (e) 49 - 16 ~ 36 = 6
(f) 1 + 36 ~ 36 = 6
(a) Over-estimate (b) Under-estimate (c) Unsure (d) Unsure (e) Unsure
(a) Under-estimate (b) Unsure (c) Unsure
(d) Unsure
(a) Over-estimate
(b) Over-estimate
(a) Under-estimate
(b) Under-estimate
(c) Under-estimate
(d) Unsure (e) Unsure
(f) Under-estimate
Key examples
Activities
Activity