Hi,

Note: The probability of x successes in n trials is: 

P = nCx*  where p and q are the probabilities of success and failure respectively. 

In this case p & q are = 1/2 or .5

nCx = 

 (a) Exactly five of the patients will return? 9C5(.5)^5(.5)^4 

 (b) All nine will return? 9C9(.5)^9

 (c) At least eight will return? 1 - 9C9(.5)^9

 (d) At least one will return? 9C0(.5)^0(.5^9) + 9C1(.5)^1(.5)^8

 (e) How many patients would be expected to return to the same dentist, i.e., what is the mean of the distribution?  

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