STANDARD DEVIATION FROM FREQUENCY TABLE WITH INTERVALS

Problem 1 :

The weekly wages (in dollars) of 90 workers in a steel yard are given alongside :

Find estimates of the mean wage and the standard deviation of the wages.

Solution :

Mean wages = 392.10

Standard deviation = 16.34

Problem 2 :

A random sample of the weekly supermarket bills for a number of families was observed and recorded in the table given.

a. Find the mean bill and the standard deviation of the bills.

b. variance of the population

Solution :

a)

Mean = 103.50

Standard deviation = 19.14

b)  Variance = 366.33

Problem 3 :

The length of 30 randomly selected 12 day old babies were measured to the nearest cm and the following data obtained.

i) Find the mean length and standard deviation of the lengths.

ii) Find the variance.

Solution :

Since the given interval is not continuous, let us make it as continuous interval.

i) Mean = 47.76, standard deviation = 2.65

ii) Variance = 7.05