A graduate student who takes 3 courses in one semester If Xt

A graduate student who takes 3 courses in one semester. If X=the number of courses with grade \"A\". The random variable X has a probability distribution as follows

x

0

1

2

3

p(x)

0.1

0.15

0.65

0.1

The probability P(X < 2) is equal to

a) 0.90

b) 0.25

c) 0.15

d) 0.65

Solution

P(X < 2) = P(X=0) + P(X=1)

               = 0.1 + 0.15

               = 0.25