Rounding to significant figures

The Maths Habit

4861 people ran a race. The newspaper says this. Is it wrong?

About 5000 people ran the race!

No. 5000 is a round number close to 4861.

A headline does not need the exact number.

Which way will the ball roll? Left or right?

left
right
right: it rolls on

Round
Change a number to a simpler number close to it.
Significant figures
The digits of a number, counted from the first digit that is not zero.

belowabove
  1. 1Ring the figures to keep.1 significant figure: ring the first digit. 2 significant figures: ring the first two.
  2. 2Find the two ends.The ringed digits, then zeros. Then one more.
  3. 3Roll to the nearer end.A ball on the very top rolls on.

Round 3620 to 1 significant figure.

1Ring the figures to keep.
Th3H6T2O0
2Find the two ends.
362030004000
3Roll to the nearer end.
Answer 4000

Round 870 to 1 significant figure.

1Ring the figures to keep.
H8T7O0
2Find the two ends.
870800900
3Roll to the nearer end.
Answer 900

Round 3620 to 1 significant figure.

1Ring the figures to keep.
Th3H6T2O0
2Find the two ends.
362030004000
3Roll to the nearer end.
Answer 4000
1Ring the figures to keep.23Roll to the nearer end.

Round 2310 to 1 significant figure.

1Ring the figures to keep.
Th2H3T1O0
2Find the two ends.
231020003000
3Roll to the nearer end.
Answer 2000

Round 3620 to 1 significant figure.

1Ring the figures to keep.
Th3H6T2O0
2Find the two ends.
362030004000
3Roll to the nearer end.
Answer 4000
1Ring the figures to keep.23Roll to the nearer end.

Round 640 to 1 significant figure.

1Ring the figures to keep.
H6T4O0
2Find the two ends.
640600700
3Roll to the nearer end.
Answer 600

Round 3620 to 1 significant figure.

1Ring the figures to keep.
Th3H6T2O0
2Find the two ends.
362030004000
3Roll to the nearer end.
Answer 4000
1Ring the figures to keep.23Roll to the nearer end.

Round 5790 to 1 significant figure.

1Ring the figures to keep.
Th5H7T9O0
2Find the two ends.
579050006000
3Roll to the nearer end.
Answer 6000

1Ring the figures to keep.23Roll to the nearer end.

1Round 8240 to 1 significant figure.

1Th8H2T4O02824080009000
3Answer 8000

2Round 360 to 1 significant figure.

1H3T6O02360300400
3Answer 400

3Round 6710 to 1 significant figure.

1Th6H7T1O02671060007000
3Answer 7000

4Round 1500 to 1 significant figure.

1Th1H5T0O02150010002000
3Answer 2000

Work these out.

5300 + 1005400
2600 + 1002700
7100 + 1007200

Round 5372 to 2 significant figures.

1Ring the figures to keep.
Th5H3T7O2
2Find the two ends.
537253005400
3Roll to the nearer end.
Answer 5400

Round 2614 to 2 significant figures.

1Ring the figures to keep.
Th2H6T1O4
2Find the two ends.
261426002700
3Roll to the nearer end.
Answer 2600

Round 5372 to 2 significant figures.

1Ring the figures to keep.
Th5H3T7O2
2Find the two ends.
537253005400
3Roll to the nearer end.
Answer 5400
1Ring the figures to keep.23Roll to the nearer end.

Round 7239 to 2 significant figures.

1Ring the figures to keep.
Th7H2T3O9
2Find the two ends.
723972007300
3Roll to the nearer end.
Answer 7200

Round 5372 to 2 significant figures.

1Ring the figures to keep.
Th5H3T7O2
2Find the two ends.
537253005400
3Roll to the nearer end.
Answer 5400
1Ring the figures to keep.23Roll to the nearer end.

Round 836 to 2 significant figures.

1Ring the figures to keep.
H8T3O6
2Find the two ends.
836830840
3Roll to the nearer end.
Answer 840

Round 5372 to 2 significant figures.

1Ring the figures to keep.
Th5H3T7O2
2Find the two ends.
537253005400
3Roll to the nearer end.
Answer 5400
1Ring the figures to keep.23Roll to the nearer end.

Round 4485 to 2 significant figures.

1Ring the figures to keep.
Th4H4T8O5
2Find the two ends.
448544004500
3Roll to the nearer end.
Answer 4500

Rounding to significant figures worksheet, page 1

Rounding to significant figures worksheet, page 2

Answer sheet

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

  1. 4721 to 1 significant figure is 5000

    Right

  2. 3640 to 2 significant figures is 36

    Wrong: it is 3600

  3. 8460 to 1 significant figure is 9000

    Wrong: it is 8000

  4. 2350 to 2 significant figures is 2400

    Right

  5. 61 to 1 significant figure is 60

    Right

  1. Round 0.0384 to 1 significant figure. Hint: start at the first digit that is not zero.

    0.04

  2. Round 2970 to 2 significant figures.

    3000

  3. Round 5.372 to 2 significant figures.

    5.4

  1. Round 5621 to 1 significant figure.

    6000
    Th5H6T2O15621

  2. Round 3740 to 2 significant figures.

    3700
    Th3H7T4O03740

  3. Round 8290 to 1 significant figure.

    8000
Exit tickets to print