Help with probability

sum of all probabilities must equal 1. so, add them and equate it to 1 but there are 2 values unknown.,.....

The sum of all probabilities must be __

with only one equation

yeah, that's why I get confused

if any one of the ??? was given, then you could have found out other ???

answer is b , but i dont know why?

:O

Impossibru!

i would have gone with D

but actually answer is B

The answer would be B if and only if the probability of getting A+, A, B+ and B is equal to the probability of getting C+, C, D, F. But that is not given in the question, so I'd go with Hartnn.

That is, 0.5

oh wait its possible :P

C+ or better = 1- (C or D or E)

P (C+ or better) = 1-P (C or D or E)) =1- (0.22+0.09+0.07)

why we choose c ,d, e ?

sorry, C,D,F

yeahh, but why?

C+ or better means A+ to C+ if we add all probabilities, we get =1 so, A+ to F = 1 (A+ to C+) + (C,D,F) =1 so, (A+to C+) = 1- (C,D,F)

oh, I got it , thank you very much

welcome ^_^

^ that.is.incorrect.

because you don't want 5 out of 8, you need probabilities of C+ or better, which needs individual probabilities. you haven't used any of the probabilities given. also, 0.62 is different from 0.625

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