How do you do this on a calculator Let X be a discrete rando

How do you do this on a calculator?

Let X be a discrete random variable taking integer values 1, 2, …, 10.
It is also known that:  P(X 4) = 0.69, P(X 4) = 0.66.
Then P(X = 4) = 0.35

Solution

Note that a probability distirbution must have all probabilities add up to 1.

hence,

P(x<=4) + P(x>=4) - P(x = 4) = 1

(we subtract P(x=4) as it was double counted when we added the first two terms.)

Hence,

0.69 + 0.66 - P(x = 4) = 1

1.35 - P(x = 4) = 1

P(x = 4) = 0.35 [ANSWER, C]