Am I being stupid again? Easy S1 question I can't do...:/ Watch

J DOT A
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Report Thread starter 7 years ago
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Hey guys,

The question is on a binomial distribution.

The random variable W has a binomial distribution B(6,0.4). Calculate the probability that the value of W is an odd number.

Now I thought that if I had a binomial, W would equal the number of success right?
So there is 1,2,3,4,5,6 Numbers I can choose.
1,3 and 5 are odd numbers

NOW WHY THE HELL do I use P(X=1)+P(X=3)+P(X=5)?
Surely P(X=1) means the probability that I get on success? So if I use P(X=2) means 3 success right?

Then why do I use P(X=1)+P(X=3)+P(X=5)?

Why don't I just use P(X=3)?

Please someone explain!
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ttoby
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Report 7 years ago
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If you want W to be odd, then you want an odd number of successes, i.e. either 1, 3 or 5 successes. Hence you want P(X=1)+P(X=3)+P(X=5)
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