FRAME 25.

The preceding problem demonstrated the calculation of a sample mean. We knew it was a

sample because the five values of interest were taken from a population of 100. We could have

computed the mean of all 100 dollar amounts. In such a case we would have had a population

mean. The difference between a sample mean and a population mean is that the population

mean includes every value in the population; whereas the sample mean includes only a portion of

the values in the population. The population mean is still the sum of the values of interest divided

by the number of values of interest. Now we are interested in the entire population.

Even though they are computed in the same manner they are different concepts and we will

need a different symbol for each. The symbol for population mean is the Greek letter u

(pronounced mu). The formula for the population mean is

u = ΣX

where,

N

X still represents each value of interest. However, we are now interested in all values in the

population)

N represents the number of items of interest in the population. Note this is a capital N rather

than the small n used in the sample mean formula.

FRAME 26.

For example, suppose the number of calculator batteries used during all ten 3-week courses

held this year is 37, 62, 28, 31, 58, 29, 35, 47, 52, and 25. We need to know the average number

of batteries used in a 3-week course this year.

a. Find the mean. __________________

b. Is this a sample or a population mean? __________________