Originally Posted by

**sadmath** Question reads: "The random variable X takes on one of the values 1,2,3,4,5 with probabilities

P(X=i) = ki, i = 1,2,3,4,5

for some value k. Find P(2 <= X <= 3)."

I'm not looking for a straight answer, just a question of where to start. I'm not sure but I thought that the sum of all P(X) across the domain of X (here [1,5]) should equal 1. So technically I should be able to solve for k right?

P(X) = kx

P(1) + P(2) + P(3) + P(4) + P(5) = 1.0

k + 2k + 3k + 4k + 5k = 1.0

14k = 1.0

k = 1/14

therefore:

P(X) = x/14

In which case the probability that X is 2 or 3 should be:

P(2 <= X <= 3) = P(2) + P(3) = 2/14 + 3/14 = 5/14