Following are the weights (in kg) of 10 newborn babies in a hospital on a particular day:
3.4, 3.6, 4.2, 4.5, 3.9, 4.1, 3.8, 4.5, 4.4, 3.6. 

Find the mean.

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

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

$\therefore$ Mean=$\frac{3.4+3.6+4.2+4.5+3.9+4.1+3.8+4.5+4.4+3.6}{10}$

$\Rightarrow$Mean=$\frac{40}{10}$= 4 kg

Therefore, the mean weight is 4 kg.