Answer:
 
Step-by-step explanation:

 
        
             
        
        
        
Answer:
a) 
And we can find this probability using the normal standard table or excel and we got:
b) 
And we can find this probability using the complement rule and the normal standard table or excel and we got:
Step-by-step explanation:
Previous concepts
Normal distribution, is a "probability distribution that is symmetric about the mean, showing that data near the mean are more frequent in occurrence than data far from the mean".
The Z-score is "a numerical measurement used in statistics of a value's relationship to the mean (average) of a group of values, measured in terms of standard deviations from the mean".  
Part a
Let X the random variable that represent the time for the step 1 and Y the time for the step 2, we define the random variable R= X+Y for the total time and the distribution for R assuming independence between X and Y is:
  
Where 
 and 
We are interested on this probability
And the best way to solve this problem is using the normal standard distribution and the z score given by:
If we apply this formula to our probability we got this:
And we can find this probability using the normal standard table or excel and we got:
Part b
And we can find this probability using the complement rule and the normal standard table or excel and we got:
 
        
                    
             
        
        
        
3 and 1 half is also known as 3.5,
3.5 x 3.5 = 12.25 
in fractions that is 12 and 1 quarter
        
                    
             
        
        
        
Answer: C. 254
Step-by-step explanation: All engineers is the population so this is stats and the number that chose math no matter what kind of engineer is 254