What do you understand by measures of dispersion? What are the different measures of depression? The following table shows the data of time taken (in seconds) for completing each one of the series of 80 similar chemical experiments.

Time(s)	50-60	61-65	66-70	71-75	76-78
Number of experiments	8	12	28	22	10

Calculate mean time experiments, standard deviation, and variance and comment on your result.