Question

The length of a text messaging conversation is normally distributed with a mean of 2 minutes and a standard deviation of .5 minutes. What is the probability that a conversation lasts longer than 3 minutes?
0.043351
0.063748
0.02275
0.095424

Answer 1

Let x be a random variable representing the length of a text messaging conversation, then
P(x > 3) = 1 - P(x < 3) = 1 - P(z < (3 - 2)/0.5) = 1 - P(z < 2) = 1 - 0.97725 = 0.02275