Estimation

The Maths Habit

About how many dots? No time to count!

19 rows

31 in a row

about 20 × 30 = 600

There are 589.

Which way will the ball roll? Left or right?

left
right
right

Estimate
A sensible answer that is close to the exact one.
≈
Round
Change a number to a simpler number close to it.
1 significant figure
Only the first digit is not zero.
00

belowabove
number ≈ nearer end
  1. 1Find the two ends.The first digit, then zeros. Then one more.
  2. 2Roll to the nearer end.This is 1 significant figure.

Round 38 to 1 significant figure.

1Find the two ends.
383040
2Roll to the nearer end.
38 ≈ 40

Round 6.7 to 1 significant figure.

1Find the two ends.
6.767
2Roll to the nearer end.
6.7 ≈ 7

Round 38 to 1 significant figure.

1Find the two ends.
383040
2Roll to the nearer end.
38 ≈ 40
12Roll to the nearer end.

Round 83 to 1 significant figure.

1Find the two ends.
838090
2Roll to the nearer end.
83 ≈ 80

Round 38 to 1 significant figure.

1Find the two ends.
383040
2Roll to the nearer end.
38 ≈ 40
12Roll to the nearer end.

Round 4.2 to 1 significant figure.

1Find the two ends.
4.245
2Roll to the nearer end.
4.2 ≈ 4

Round 38 to 1 significant figure.

1Find the two ends.
383040
2Roll to the nearer end.
38 ≈ 40
12Roll to the nearer end.

Round 712 to 1 significant figure.

1Find the two ends.
712700800
2Roll to the nearer end.
712 ≈ 700

12Roll to the nearer end.

1Round 58 to 1 significant figure.

1Find the two ends.
585060
2Roll to the nearer end.
58 ≈ 60

2Round 2.3 to 1 significant figure.

1Find the two ends.
2.323
2Roll to the nearer end.
2.3 ≈ 2

3Round 91 to 1 significant figure.

1Find the two ends.
9190100
2Roll to the nearer end.
91 ≈ 90

4Round 286 to 1 significant figure.

1Find the two ends.
286200300
2Roll to the nearer end.
286 ≈ 300

Work these out.

3 × 2060
4 × 50200
20 × 30600
80 ÷ 420

belowabove
nearer end×nearer end
=estimate
  1. 1Find the two ends.The first digit, then zeros. Then one more.
  2. 2Roll to the nearer end.This is 1 significant figure.
  3. 3Work it out.Use the rounded numbers. This is the estimate.

Estimate 4.2 × 39.

1Find the two ends.
4.245393040
2Roll to the nearer end.
4×40
3Work it out.
=160

Estimate 2.9 × 51.

1Find the two ends.
2.923515060
2Roll to the nearer end.
3×50
3Work it out.
=150

Estimate 4.2 × 39.

1Find the two ends.
4.245393040
2Roll to the nearer end.
4×40
3Work it out.
=160
12Roll to the nearer end.3Work it out.

Estimate 5.1 × 62.

1Find the two ends.
5.156626070
2Roll to the nearer end.
5×60
3Work it out.
=300

Estimate 4.2 × 39.

1Find the two ends.
4.245393040
2Roll to the nearer end.
4×40
3Work it out.
=160
12Roll to the nearer end.3Work it out.

Estimate 79 ÷ 3.8.

1Find the two ends.
7970803.834
2Roll to the nearer end.
80÷4
3Work it out.
=20

Estimate 4.2 × 39.

1Find the two ends.
4.245393040
2Roll to the nearer end.
4×40
3Work it out.
=160
12Roll to the nearer end.3Work it out.

Estimate 3.2 × 198.

1Find the two ends.
3.234198100200
2Roll to the nearer end.
3×200
3Work it out.
=600

Estimation worksheet, page 1

Estimation worksheet, page 2

Answer sheet

Is it right?
Thumbs up: right. Thumbs down: wrong.

  1. 4.9 × 21 is about 100

    Right

  2. 312 to 1 significant figure is 310

    Wrong: it is 300

  3. 6.8 × 29 is about 210

    Right

  4. 2.2 × 48 is about 100

    Right

  5. 61 ÷ 2.9 is about 30

    Wrong: 60 ÷ 3 = 20

  1. Estimate (18.9 + 41.2) ÷ 5.8.

    (20 + 40) ÷ 6 = 10

  2. Estimate 0.48 × 612. Hint: 0.48 is between 0.4 and 0.5.

    0.5 × 600 = 300

  3. Estimate 3.9 × 5.2 × 7.8.

    4 × 5 × 8 = 160

  1. Estimate 5.9 × 31.

    180
    5.956313040×=

  2. Estimate 8.2 × 19.

    160
    8.219×=

  3. Estimate 61 ÷ 2.9.

    20
Exit tickets to print