binomial prob. qn (1 Viewer)

[nick90]

gday i've got a question regarding binomial probability from Fitzpatrick ex 29(b), Q8.

The question is: A dental inspector finds that about 20 % of children of a certain area have tooth decay. What is the probability that out of the 6 children examined, only the first, third and fifth have tooth decay.

I think that the answer is 0.2^3 x 0.8^3 = 64/15625
However, Mr Fitzpatrick believes the answer to be 64/3125.

Have I made a mistake? If I have I just can't find it!

Thanks for your help in advance.

 

[independantz]

You forgot to take into account the number of awys of choosin gthe kids.

6C3-(5C1x3C1x1C1)=5

5x64/15625=64/3125

 

[nick90]

i dont get what you mean. what has choos ing the kids got to do with it?

 

[independantz]

It's a probability question, thus, the number of ways of choosing the kids is also a determinant in the final answer. Try looking through some of the worked examples in the fitzpatrick book.