**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

Go back to your answers to the worksheet.

State and justify which are over-estimates, which are under-estimates.

Are there any you can't be certain of?

Main Activity 1 Answers

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.

Main Activity 1 Answers

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**

Answers

Answers