There are two methods. MethodAhas a mean of 31 minutes and a standard deviation of 2 minutes, while methodBhas a mean of 35 minutes and a standard deviation of 1.0 minutes.

a) which is preferred if the procedure must be completed in 30 minutes?

b) which is preferred if the procedure must be completed in 38.0 minutes?

c) which is preferred if the procedure must be completed in 37 minutes?

Using z= x-u

s s= Standard deviation

I got:

a) Method A= -.5

Method B= -.2.5

b) Method A = 3.5

Method B = 3

c) Method A = 3

Method B = 2

But is there another step I'm missing?