how many of these people would have I.Q.s below 67?

Question

A standard I.Q. test produces normally distributed results with a mean of 100 and a standard deviation of 15 for the city of New York. Out of approximately 8,400,000 citizens, how many of these people would have I.Q.s below 67?

Answer 1

Obtain a z-table: http://users.stat.ufl.edu/~athienit/Tables/Ztable.pdf

 

z = (67 - 100) / 15

z = -33 / 15

z = -2.2

 

1.39% of 8400000

 

What is that?