Hi everyone!

So, my problem is:

Let X be birth weight of a randomly chosen child in Norway, given in gram, g. Assume that

X is normally distributed, where E(X) = 3315 and Var(X) = 575^{2}

.

a) Calculate the following probabilities,

1) P(X > 3000) 2) P(3000 < X < 3500) 3) P(X > 3500 | X > 3000)

What I have done to solve it:

So, I managed to get the right answer on 1, and I thought I would get the right answer on number 2.

I thought: P(3000 < X < 3500) = P(X > 3000) ∩ P(X < 3500). In 1) I calculated that P(X > 3000) is 0,709, this was correct. I calculated that P(X < 3500) = 0,6235. So 0,709 x 0,6235 = 0,4421 , but the right answer is: 0,335. What am I doing wrong?

Thanks for taking a look!