PDA

View Full Version : Answer is wrong


waqassiddiqui
Feb 20, 2008, 10:27 AM
Q- Two cards are drawn in succession from a deck without replacement. What is the probability that both cards are greater than 2 and less than 8?

My solution:
probabilty = n/N
n = 5 x 4
N = 52 cards
probability = 20 / 52


BUT the answer is 95/663

ISneezeFunny
Feb 20, 2008, 10:48 AM
you got the first step down.

there are 5 cards (per suit) that's between 2 - 8. (3, 4, 5, 6, and 7)

there are 4 suits.

so there are 20 cards out of 52 cards that you're looking for. That's for the FIRST pick.

20/52

second pick, you are left with 19 cards out of 51 cards.

19/51

(20/52)(19/51) = 95/663

galactus
Feb 22, 2008, 12:07 PM
That's a nice explanation given by I sneezefunny. You can also use combinations.

\frac{C(20,2)}{C(52,2)}=\frac{95}{663}