Measurements are rarely exactly the same each time. Repeating a measurement and calculating the mean gives a better value. To find the mean, add the repeat results and divide by how many there are. Three results of 12, 14 and 13 cm give a mean of 39 ÷ 3 = 13 cm.
The range of the repeats is the biggest minus the smallest. A small range means the repeats are close together, so the results are repeatable. A large range means something varied between the repeats, and you should be less sure of the mean.
Worked example
Repeats were 20 s, 22 s and 24 s. What are the mean and range?
- Mean = (20 + 22 + 24) ÷ 3 = 66 ÷ 3 = 22 s.
- Range = 24 − 20 = 4 s.
Answer:Mean 22 s, range 4 s.
Key words
- repeat
- do a measurement again
- mean
- total ÷ number of values
- range
- biggest value minus smallest value
- repeatable
- similar results when repeated
Practise this
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