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# S2 Hypothesis Testing Help Watch

1. I wonder if you can help. I am working through a question and I don't understand how the answer was reached. It is X~B(10,0.68) with a 5% significance and X=3. So I have calculated X=0 + X=1 + X=2 + X=3
.32*10 +10(0.68)(0.32*9)+5(0.68*2)(0.32 *8)+10/3(0.68*3)(0.32*7)

but the answer is saying that instead of 5 and 10/3 I should have 45 and 120 but I don't understand why?

Thanks
2. (Original post by Catful1)
I wonder if you can help. I am working through a question and I don't understand how the answer was reached. It is X~B(10,0.68) with a 5% significance and X=3. So I have calculated X=0 + X=1 + X=2 + X=3
.32*10 +10(0.68)(0.32*9)+5(0.68*2)(0.32 *8)+10/3(0.68*3)(0.32*7)

but the answer is saying that instead of 5 and 10/3 I should have 45 and 120 but I don't understand why?

Thanks
The binomial coefficient is . Note the factorials.

So for instance in your third term where you have 5. We have n=10 (which is true for all the terms here), and r=2.

Hence 10!/(2!8!) = 10x9/2 = 45.
3. (Original post by Catful1)
So I have calculated X=0 + X=1 + X=2 + X=3
.32*10 +10(0.68)(0.32*9)+5(0.68*2)(0.32 *8)+10/3(0.68*3)(0.32*7)
You have to use factorials i.e. X = 0 is 10C0, X = 1 is 10C1, etc...

Also, it should be 0.68^1, 0.68^2, etc.. and 0.32^10, 0.32^9...

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Updated: April 12, 2013
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