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There are different ways of working out the average of a set of numbers. This problem looks at using the mean. The mean is worked out by adding up the set of numbers and dividing the answer by how many numbers there are.

For example, the mean of the numbers 2, 3, 4, and 5 is (2+3+4+5)/4 = 3.5

Three students had collected some data for a project about bats. Each had collected a different set of readings for the wingspan of some bats. Unfortunately, each student had lost one measurement.

Two of the students had already added up their data and worked out their individual means and the overall mean was also known. The known information is summarised below:

Student A had collected 5 measurements, the others had each collected 6.

Student Data set (wingspans in cm) Mean (cm)

A 12 10 16 14 - 15   13
B 13 12 - 12 14 17 16 14
C 11 14 15 - 11 13 12 -

The overall mean from the combined data = 13.35 cm Using the above information can you complete the table?