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# S2 Binomial help!!!!!

Maths and statistics discussion, revision, exam and homework help.

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1. S2 Binomial help!!!!!
This is a question from the june 2005 paper, question 7
here there is binomial distribution x~B(20,0.75)

p(x<or equal to 13)=1-0.7858=0.2142
how did they find this out, did they do (p20 + p=19.....)
I DON'T KNOW HOW TO SOLVE BIG X VALUES WHEN P IS NOT IN THE TABLE BUT N IS, because if you did have to use the manual formula that would take ages
so how do you do it

i know you can use 0.25 as p, but i want to know how to do it using p as 0.25
as some question have come up where you use p as 0.23 and therefore you can't use that method as either way p is not in the table
thanks
2. Re: S2 Binomial help!!!!!
Well yeah, as you've said, use p=0.25 and define a new random variable, e.g. Y. And if any questions come up with a value for p that isn't in the tables then you'll just have to work it out by plugging the numbers into the equation, but n won't be very big for those questions so it won't be too tedious.

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