DSE 2009

[reetika05]

Hi Sir,

Can you please help me out with this question..
Q 37. Jai and Vijay are taking a exam in statistics. The exam only has three grades A, B and C. The prob that Jai gets a B is 0.3, the prob that Vijay gets a B is 0.4, the prob that neither get an A, but atleast one gets a B is 0.1. What is the prob that neither gets a C but atleast one gets a B?  

[Amit Goyal]

In what follows, I am going to write Jai's grade first followed by Vijay's grade. For example if i mention the sample point AB that would mean that Jai's grade is A and Vijay's grade is B.
Pr(Jai gets a B) = Pr(BA, BB, BC) = Pr(BA) + Pr(BB) + Pr(BC) = 0.3 ---(1)
Pr(Vijay gets a B) = Pr(AB, BB, CB) = Pr(AB) + Pr(BB) + Pr(CB) = 0.4 ---(2)
Pr(Neither gets an A, but at least one gets a B)
= Pr(BC, BB, CB) = Pr(BC) + Pr(BB) + Pr(CB) = 0.1 ---(3)
Pr(Neither gets an C, but at least one gets a B) = Pr(BA, BB, AB) = Pr(BA) + Pr(BB) + Pr(AB) = 0.6 (Add (1) and (2) and then subtract (3) from it)

[reetika05]

Thank you sir..

[aditi5000]

Thank you SIr!!!