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# s1 conditional prob. q watch

1. guys here in part C .. i know its a conditional probability but how do we find the numerator?? (the intersection)
2. (Original post by pondsteps)
guys here in part C .. i know its a conditional probability but how do we find the numerator?? (the intersection)
Well what scenarios/combinations result in the die being rolled twice and the final score being three?
3. (Original post by ghostwalker)
Well what scenarios/combinations result in the die being rolled twice and the final score being three?
P(T=3) intersection die rolled twice / P die rolled twice

i mean how do i find the intersection??
4. (Original post by pondsteps)
P(T=3) intersection die rolled twice / P die rolled twice

i mean how do i find the intersection??
That is what my question was addressing. You need to look at the possible scenarios.

e.g if first roll is 3, then it's not rolled twice, so that's not part of the event.

IF first roll is 2, then the second roll must be ?

Etc.
5. (Original post by ghostwalker)
That is what my question was addressing. You need to look at the possible scenarios.

e.g if first roll is 3, then it's not rolled twice, so that's not part of the event.

IF first roll is 2, then the second roll must be ?

Etc.
ohhhh ok got it... here in the last question ... im just stuck on how to find the intersection between B and C
6. (Original post by pondsteps)
ohhhh ok got it... here in the last question ... im just stuck on how to find the intersection between B and C
Given P(C' n B') = 0.3

What's the complementary event, and you should be able to work out P(BnC) from that with the other information given.
7. (Original post by ghostwalker)
Given P(C' n B' = 0.3

What's the complementary event, and you should be able to work out P(BnC) from that with the other information given.
how does that help us find the intersection?? so we do P(B u C)' = P(B)' + P(C)' - P(BnC)'??? is that how it works or not.... i didnt know how to deal with the prime
8. (Original post by pondsteps)
how does that help us find the intersection?? so we do P(B u C)' = P(B)' + P(C)' - P(BnC)'??? is that how it works or not.... i didnt know how to deal with the prime
(B' n C') = (B u C)'

They are not complementary events, they are the same event.

The complementary event is B u C

And P(B u C) = 1-0.3 = 0.7

Now do the same with that.
9. (Original post by ghostwalker)
(B' n C' = (B u C)'

They are not complementary events, they are the same event.

The complementary event is B u C

And P(B u C) = 1-0.3 = 0.7

Now do the same with that.
what do u mean by complemntary events???? is the rule i write out correct or wrong???
10. (Original post by pondsteps)
what do u mean by complemntary events???? is the rule i write out correct or wrong???
You should know what complementary events are - check your textbook.

What you wrote is incorrect, even the notation.

P(B u C)' should be P( (B u C)' )

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