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
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