Question 1130970
Find probability no defective cards are and subtract from one.
(6/21)(5/20)(4/19)(3/18)=(2/7)(1/4)(4/19)(1/6)=2/798=1/399
398/399 is the probability at least one card is defective.

(7/21)(6/20)(5/19)(4/18)=(1/3)(3/10)(5/19)(2/9)=1/171
so the probability is 1-1/171 or 170/171