The following are the results of measurements taken at intervals over a half cycle of alternating voltage:

Time (t milliseconds) 0 0.45 0.95 1.5 2.1 2.5 3.1 3.9 4.5 5.0

Voltage (V volts) 0 20 36 40 37.5 33 32 31 20 0

Calculate the r.m.s. value, average value and frequency of the wave. (16)