Average

Average is some time called arithmatic mean and denoted by AM.

AM/Average = Sum of all observations / Number of Observations

We can re-arrange the above formula to find out sum of all observtions, if number of observations and average is given.

Sum of all observations = Average / Number of observations

Similarly, we can re-arrange the formula to find number of observtions if sum of all observation and average of numbers is given.

Number of observations = Sum of all obserations / Average

Example: Find the average of 5, 8, 7, 9, 11

Solution:

Sum of all observations:   5 + 8 + 7 + 9 + 11 = 40

Total numbers of observations = 5

Average = 40 / 5 = 8

Example: Sum of observation is 40, and average is 8, find number of observations.

Number of observations = 40 / 8 = 5 

Example: Number of observation is 5, and average is 8, find sum of observations.

Sum of observation = 5 * 8 = 40