It is given here that there is 1/3 probability of professional baseball player will get a hit. Hence if at least three hits are gained out of 5 attempts, the calculation goes: 5C3 (1/3)^3(2/3)^2 + 5C4 (1/3)^4(2/3)^1 +5C5 (1/3)^5(2/3)^0 equal to 0.21.
