The measure of central tendency that was used to find the average is the mean.
A mean is a quantity that has a value intermediate between those of the extreme members of some set. It is an average of the set of numbers.
The mean equals the sum of a set of numbers divided by the count which is the number of the values being added. In this case, Sara should calculate the bill divided by the total number of minutes to get the amount spent on each call every minute.
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