An aircraft has 120 passenger seats. The number of seats occupied during 100 flights is given in the following table.

Determine the mean number of seats occupied over the flights.

We first, find the class mark of each class and then proceed as follows.

∴ Assumed mean, a = 110

Class width, h = 4

and total observations, N = 100

By step deviation method,

=

But seats cannot be in decimal, so number of seats is 109.