What is the mean of the first 10 prime numbers?

Mean refers to the average of a collection of values and it is given by: 

Mean =$\frac{\mathrm{Sum} \mathrm{of} \mathrm{the} \mathrm{observations}}{\mathrm{Number} \mathrm{of} \mathrm{the} \mathrm{observations}}$

The first 10 prime numbers are: 2, 3, 5, 7, 11, 13, 17, 19, 23, 29

$\Rightarrow$ Mean= $\frac{2+3+5+7+11+13+17+19+23+29}{10}=\frac{129}{10}=12.9$

Therefore, '12.9' is the correct response.