HW2 solutions: 

Problem 2. P(systerm fails)=P(all four components fail)=(1-0.85)**4=0.000506

4.24 P(A)=192/(192+248)=0.436
     P(B)=(48+80)/440=0.291
     P(A and B)=48/440=0.109

4.25 (a) Any one of these is OK: 
     Since P(A)*P(B)=.127, which is not equal to P(A and B)=0.109,
     Thus, A and B dependent. 
OR:  Since P(B|A)=48/192=0.25, which is not equal to P(B)=0.291,
     Thus, A and B dependent.
OR:  Since P(A|B)=48/128=0.375, which is not equal to P(A)=0.436,
     Thus, A and B dependent.

     (b) P(B|A)=48/192=0.25
         P(B|not A)=80/248=0.323
         In general, P(B|A) is not equal to P(B|not A). 

Problem 4. Minitab:

(a) Descriptive Statistics: Donors

Variable             N       Mean     Median     TrMean      StDev    SE Mean
Donors              20     317.80     317.50     317.78      36.62       8.19

Variable       Minimum    Maximum         Q1         Q3
Donors          250.00     386.00     296.50     334.00