The prob. that Candela will score above 90 on a test is 4/5.

Question

What s the prob. that shell score above 90 3 out of 4 tets this quarter?

Answer 1

This is a binomial distribution  B(n,p)  with parameters  n = 4  tests and  p = 4/5  probability of scoring above 90  

 

The probability of getting exactly k successes out of n trials is given by  

 

P(X=k) = _nC_k * p^k * (1-p)^n-k   

 

where  _nC_k is the binomial coefficient = n!/(k!(n-k)!)  

 

Plug in 3 for k, 4 for n, and 4/5 for p