It can't be 8, you are correct it should be
Got my AS level stats test soon and do not understand one of the past paper questions.
The Distances travelled to work, Dkm, by the employeed at a large company are normally distributed with D-N(30,82) ..... so mean of 30 and variance of 82?
Find the probability that a randomly selected employee has a journey to work of more than 20km.
The mark scheme says
P(D > 20) = P(Z > 20-30/8)
Where did they get the divide by 8 from? I thought it was sqrt(82)
Any help would be great thanks.