Math Is Fun Forum

morik

Member

Registered: 2005-11-23

Posts: 16

binomial function

Another one I'm struggling with...

A group of 18 students is composed of 7 Chinese, 5 British and 6 Indian students. None of these students has multiple citizenship.

In your answer to the following question you may use the function binomial. The binomial coefficient,

which denotes the number of ways of selecting k objects out of n, is input as binomial(n,k)

What is the probability of selecting 2 Chinese students from this group?

It's hurting my brain. How do I work that out??

George,Y

Member

Registered: 2006-03-12

Posts: 1,379

Re: binomial function

suppose each combination of two students from the 18 share the same probability.
Since the number of the combinations is binominial(18,2), the probability for each one should equally be  1/binominial(18,2).
The number of ways of selecting 2 Chinese is binomial(7,2), and each way has  1/binominial(18,2)  chance to appear in the random selecting 2 out of 18 process. Hence the total chance (added together) should be:
binomial(7,2) ×1/binominial(18,2)=binomial(7,2) /binominial(18,2)

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X'(y-Xβ)=0