what is the basis for assuming a small sample 10 pieces or l

what is the basis for assuming a small sample (10 pieces or less) is normal

Solution

If a random variable is affected by many independent causes and the effect of each cause is not overwhelmingly large compared to other effects, then the random variable will closely follow a normal distribution.

Eg. The lengths of pins made by an automatic machine the weight of baseballs, the time taken by an assembly worker to complete the assigned task repeatedly etc.

We generally assume that if number of samples are less than or equal to 30, they will follow normal distribution, otherwise t distribution.