Question 1025786
a. Let X = # of items that are defective.  The r.v. X follows the binomial distribution.

==> {{{P(X >3) = 1-P(X <= 3) = 1-P(0)-P(1)-P(2)-P(3) = 1-C(25,0)*0.93^25*.07^0 -
C(25,1)*0.93^24*.07^1 -C(25,2)*0.93^23*.07^2 -  C(25,3)*0.93^22*.07^3 = 0.0936}}}, to four decimal places. 

b.  Let X = the number of trials in getting the first defective item.
This r.v. follows the geometric distribution with support 1,2, 3, 4, 5,... .
The mean of the geometric distribution where the probability of success is p = 0.07 (in this case getting a defective item) is 1/p = 1/0.07 = 14.2857, or 14 items.