GCSE Maths revision · Probability and statistics
The mean is the total divided by how many; the median is the middle value in order; the mode is the most common; the range is largest minus smallest. For grouped data, use each class midpoint to estimate the mean.
Watch out Divide by the total frequency, not by the number of rows in the table.
A shop records the number of umbrellas it sells each day. The table shows the results.
| Number sold | Frequency |
|---|---|
| 0 | 3 |
| 1 | 8 |
| 2 | 5 |
| 3 | 2 |
Write down the mode.
Answer
These are the lengths, in centimetres, of seven pieces of ribbon. 12, 7, 16, 9, 20, 11, 15 Work out the median length.
The table shows information about how long 20 customers waited for a delivery.
Work out an estimate for the mean waiting time.
| Waiting time (t minutes) | Frequency |
|---|---|
| 0 < t ≤ 10 | 6 |
| 10 < t ≤ 20 | 9 |
| 20 < t ≤ 40 | 5 |
Two groups of readings are combined. The first group contains n readings with mean 24. The second group contains n + 4 readings with mean 32. The mean of all the recorded readings is 29. One reading in the first group was recorded as 38, but should have been 14. Work out the mean of all the readings after this error is corrected.
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