Solution of problem N1731 Laplace probability theory

Solution of problem N1731 Laplace probability theory

1731. It is known that 3/5 of shoes made by the factory are valued as 1st class products. What is the probability that among the randomly taken 400 pairs of shoes manufactured by the factory, the 1st grade will be:
1) 250 pairs;
2) from 250 to 300 pairs

Additional information:

Detailed solution. Decorated in Microsoft Word 2003 (Quest decided to use the formula editor)