Solution of problem N836 Laplace probability theory

836. In the advanced scientific laboratory, it was possible to cross potatoes with pineapple. Unfortunately, the seedlings of such a promising plant do not take root well - only one starts from 10. Yunnat from the sponsored circle helps scientists in their outstanding studies. They planted 400 amazing plants. Find the probability that soon the harvest will be: a) exactly 60 of them; b) not less than 60; c) at least 25 plants; d) from 30 to 50 plants.