probability of something

Statistics
Tutor: None Selected Time limit: 1 Day

  Score                     A           B           C        D        F     Total

0-10

8

11

5

18

41

83

11-20

29

45

80

26

11

191

21-30

50

62

42

20

4

178

31-40

47

62

31

6

10

156

Column Totals

134

180

158

70

66

608

 

 

a)  What is the probability that a student will get a “B”?

b)    What is the probability that a student will get an “A” given that a score of 21-30 was achieved on the placement test?

c)   probability that a student scored between 11-20 and got a B in the course?

probability student got b/t 11-20 knowing they got B in clas

 

Jun 2nd, 2015

Thank you for the opportunity to help you with your question!

a) Number of people getting B is 180 on a total of 608 so p=180/608=0.296

b)There are 178 students having a score between 21 and 30 and 62 of them get B so p=62/178=0.348

c)Let's call B : student score 11-20 and A : student get B 

p(A inter B)=45/608=0.074

p(A inter B)=P(A)*Pa(B) (Pa(B) = probability getting 11-20 knowing getting B)

Pa(B)=p(A inter B)/P(A)=0.074/0.296=0.25

Please let me know if you need any clarification. I'm always happy to answer your questions.
Jun 2nd, 2015

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