1. Since z=(28-20)/5=1.6 then the proportion is (100-89.04)/2=5.5%.

2. Since the rise=-100{0.6(5/150)}=-2 then the number of failures is 18.

3. Since b=0.6(5/150)=0.02 and a=20-0.02(1200)=-4 then the regression
equation is:
             # of failures = -4 + 0.02(size)

4. Slope: For unit increase in size you can expect # of failures to increase
by 0.02 (alternatively, for an increase in size of 50LOC you can expect one
additional failure).
   Intercept: when size is zero then # of failures is -4. this is not
meaningful.

5. Since the mean (from above) is 18 we only need to determine SD(y|x)
before applying normal theory. SD(y|x)=5(sqrt(1-0.36))=4. Hence z=(28-18)/4
which is 2.5 and so the proportion is (100-98.76)/2=0.6%.