In one month the total costs (to the nearest pound) of the calls made by 23 female mobile phone owners were 14 5 15 6 17 10 22 10 12 17 13 29 7 27 33 16 30 9 15 7 33 28 21 Find the median and upper and lower quartiles for this distribution.

Array 5 6 7 7 9 10 10 12 13 14 15 15 16 17 17 21 22 27 28 29 30 33 33 The median position = (23 + 1)/2 = 12th position, so the median value is the value ‘15’.

This suggests that the monthly cost of calls for half the female owners is below £15, and the monthly costs for the other half is above £15.

The quartile position = (12 +1)/2 = 6.5th position, that is midway between the 6th and 7th observations.