Answer:
Mendel used large sample size in his experiments to establish the inheritance rules of nature as he studied different characters of pea plants and used mathematical models and formulas like probability methods and punnet square method for the mono and di-hybrid crosses.
The large sample size helped him evaluating his principles as:
1. large sample size provided a more accurate mean value
2. study the outliers or the data which can affect the data in a small sample
3. provided a small margin of error.
Since he applied mathematical methods in identifying and establishing the rules he required a large sample size to study.