5 The figure below summarises the time taken by a group of 100 students to solve a series of problems.
(a) Copy and complete the frequency table given below. The first frequency is already included.
t f
5 <= t < 12 28
12 <= t < 16
16 <= t < 20
20 <= t < 30
(b) Estimate the mean time.
(c) Estimate the standard deviation of the times.
(d) Estimate, using linear interpolation, the median of the times.
(e) Give a reason why your answers to (b)-(d) are not exact.