The speed limit outside a school is 40 km / h. Year 11 students measured the speed of passing vehicles over a period of time. They found the set of data to be normally distributed with a mean speed of 36 km / h and a standard deviation of 2 km / h.

Question

What percentage of the vehicles passed the school at a speed greater than 40 km / h?

The answer is 2.5%, though I am not sure how to get this.

Answer 1

z-score for your event = (40 - 36)/2 = 2
I don't know if you use tables or some other means to find
the answer.
If you have tables, find 2.0 in the left column and you should see
.9772 or 97.72%
This is the percentage that would have below 40 km/h
So the percentage above 40 km/h would be 100% - 97.72^ = 2.28%

I got my results here:
http://davidmlane.com/normal.html