# Math Help - Normal Distribution

1. ## Normal Distribution

Hi, I'm having a bit of trouble with this question.

The fuel consumption of a ﬂeet of 150 lorries is approximately normally distributed with mean 15 mpg and sd 1.5 mpg.

(ii) What is the probability that the average consumption of a random sample of four lorries exceeds 16 mpg?

I have an idea on how to solve the question, by using the standard normal distribution but how do I take into account that the question is asking for the consumption of four lorries, rather than 150?

2. Originally Posted by blueturkey
Hi, I'm having a bit of trouble with this question.

The fuel consumption of a ﬂeet of 150 lorries is approximately normally distributed with mean 15 mpg and sd 1.5 mpg.

(ii) What is the probability that the average consumption of a random sample of four lorries exceeds 16 mpg?

I have an idea on how to solve the question, by using the standard normal distribution but how do I take into account that the question is asking for the consumption of four lorries, rather than 150?

The distribution of the sample mean is normal with the same mean as the population and SD equal to the population SD divided by the square root of the sample size.

CB

3. Thanks, thats exactly the step I was missing