A pet groomer has 7 animals to groom for the day (2 cats and 5 dogs). If she randomly selects 4 animals to groom before lunch, what is the probability she will finish all the cats before lunch?	Choose the correct choice from the following
A) 3 / 7 B) 2 / 7 C) 12 / 13 D) 5 / 11 E) 4 / 7

Rationale: combination probability formula : ncr = n ! / [ r ! ( n - r ) ! ] total possible , select 4 animals from 7 animals = 7 c 4 = 7 ! / [ 4 ! ( 7 - 4 ) ! ] = 35 . to finish all 2 cats there must be 2 dogs , select 2 dogs from 5 = 5 c 2 = 10 . and , select 2 cats from 2 = 2 c 2 = 1 . 2 cats and 2 dogs = ( 1 ) ( 10 ) = 10 probability = ( number outcomes favorable ) / ( total number outcomes ) = 10 / 735 = 2 / 7 answer : b
Answer: B