Part over total is how you do it
The length<span> of a </span>social media interaction<span> is </span>normally distributed<span> with a </span>mean<span> of </span>3 minutes<span> ... The </span>length<span>of a </span>social media interaction<span> is </span>normally distributed<span> with a </span>mean<span> of </span>3 minutes<span> and a </span>standard deviationof .4 minutes<span>. </span>
What exactly is the question? I dont see any