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?

Answer 1

Let $x$ be a random variable which represents the length of a text messaging conversation $\Rightarrow$ $P(x\ \textgreater \ 3)=1-P(x\ \textless \ 3)=1-P(z\ \textless \ \frac{3-2}{0.5})=1-P(z\ \textless \ 2)=$$1-0.97725=0.02275$.