# Mean

Arithmetic mean is the average of numbers i.e. the sum of all observations in the data divided by the number of observations.

Arithmetic mean =

Thus if x_{1}, x_{2}, x_{3 }â€¦ x_{n} be n numbers, their arithmetic mean or simply mean, is given by,

=

And n= x_{i} =

The marks obtained by 5 students out of 100 are given as 95,71,87,48 and 98 respectively. Find the mean marks per student.

The given marks are 95, 71, 87, 48 and 98.

Here n = 5

= 95 + 71 + 87 + 48 + 98 = 399

.^{.}. Average of mean () = = × 399 = 79.8

The mean of 10 numbers is 20. If 5 is subtracted from every number, what will be the new mean.

Mean of 10 numbers = 20

∴Sum of 10 numbers = 10 ×20 = 200

After subtracting 5 from every number, new sum = 200 - 10 ×5 = 150

New mean = 150/10 = 15.