SOLUTION: The time required to make 1100 gallons of synthetic rubber at a plant in South America in a recent year was normally distributed with a mean of 16 hours and a standard deviation of

[Notice that the "1100 gallons" has nothing to do with the problem]

We calculate the z-score for 19







We draw the normal curve and shade under the curve
to the right of z=1:
 

 
The percentage of the area that is shaded is what we are after.

Now you've probably learned that 34.1% of the area under
the normal curve lies between z=0 and z=1 and that 50% of 
all of the area under the normal curve lies to the right 
of z=0.  So subtracting the 34.1% of the area between
z=0 and z=1 from 50% gives the percent of shaded area,
which is the probability that it will take more that 19
hours.  50%-34.1% = 15.9% is the desired probability, or,
expressed as a decimal, 0.159.

Edwin