Suppose there are 40 students in a class and their blood typesare as follows: 45

Question

Suppose there are 40 students in a class and their blood typesare as follows: 45% has type O; 40% has type A; 10% has typeB; and 5% has type AB. a) If we randomly select two students from this class, what isthe probablity that both have the same blood type? b) If we randomly select two students from this class and itis observed that the first student's blood type is B. What is theprobability that the second student's blood type is O? Note: Will give an excellent rating to those who answer thisquestion correctly. Suppose there are 40 students in a class and their blood typesare as follows: 45% has type O; 40% has type A; 10% has typeB; and 5% has type AB. a) If we randomly select two students from this class, what isthe probablity that both have the same blood type? b) If we randomly select two students from this class and itis observed that the first student's blood type is B. What is theprobability that the second student's blood type is O? Note: Will give an excellent rating to those who answer thisquestion correctly.

Explanation / Answer

first we will calculate the no. of students having blood typeO,A,B,AB out of 40 students 45% have type O thus there are 40*0.45=18 students having blood type O similarly there are 40*0.4=16 students having blood typeA 40*0.1=4 students having blood type B and 40*0.05=2 students having blood type AB a)we need to find the prob. tht both students selected havesame blood type {note : two students are choosen withoutreplacement} Prob. tht both students have blood type O or A or B orAB Prob. tht both students selected have blood typeO=18/40*17/39 {since first sudent is selected there are 39 left in the classand out of 39 only 17 have blood type O} similarly Prob. tht both students selected have blood typeA=16/40*15/39 Prob. tht both students selected have blood typeB=4/40*3/39 Prob. tht both students selected have blood typeAB=2/40*1/39 thus Prob. tht they have same blood type is18*17  + 16*15   +4*3    +     2                                                                     40*39       40*39   40*39     40*39 P(both students selected have same bloodtype)=560/1560=56/156 b) If we select two students and observe tht one student hasblood type B we have to find the Prob. tht the second students blood typeis O if one student is observed B then out of 39 studentsthere are 18 students with blood type O so P(of second student is O given first student isB)=18/39 hope this helps                                                                  40*39       40*39   40*39     40*39 P(both students selected have same bloodtype)=560/1560=56/156 b) If we select two students and observe tht one student hasblood type B we have to find the Prob. tht the second students blood typeis O if one student is observed B then out of 39 studentsthere are 18 students with blood type O so P(of second student is O given first student isB)=18/39 hope this helps b) If we select two students and observe tht one student hasblood type B we have to find the Prob. tht the second students blood typeis O if one student is observed B then out of 39 studentsthere are 18 students with blood type O so P(of second student is O given first student isB)=18/39 hope this helps

Related Questions

Navigate

• Browse (All)
• Browse S
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.