Jenny's ballet class is going to the finals of a ballet competition. There are 25 people in her class. But for the finals group, only 10/25 (2/5) of the class is in that group. What is the probability that Jenny and her 3 best friends will be chosen?
There are C(25,10) = 3268760 different groups possible
Jenny and her three best friends comprise a partial group....to fill out the remaining spots we can choose any 6 of the 21 remaining people = C(21,6) = 54,264 posiible groups containing Jenny and her three best friends
So......the probability of this happening =
54264 / 3268760 = 21/1265 ≈ 0.0166 ≈ 1.66 %