Probability- spades, kings, queens

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ikaplan: Master | Next Rank: 500 Posts; Posts: 181; Joined: Fri Sep 04, 2009 12:06 pmFollowed by: 1 member; Thanked: 17 times

by ikaplan » Thu Sep 08, 2011 1:58 pm

If a card is picked up at random from a pack of 52 cards, find the probability that it is a 'spade' or a 'king' or a 'queen'.

(A) 21/52
(B) 5/13
(C) 19/52
(D) 15/52
(E) None of these

Source: Quantitative Aptitude CAT (Arun Sharma)

"Commitment is more than just wishing for the right conditions. Commitment is working with what you have."

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Source: Beat The GMAT — Problem Solving | Thu Sep 08, 2011 1:58 pm

n@resh: Senior | Next Rank: 100 Posts; Posts: 61; Joined: Tue Apr 13, 2010 3:29 am; Thanked: 8 times

by n@resh » Thu Sep 08, 2011 3:14 pm

ikaplan wrote:If a card is picked up at random from a pack of 52 cards, find the probability that it is a 'spade' or a 'king' or a 'queen'.

(A) 21/52
(B) 5/13
(C) 19/52
(D) 15/52
(E) None of these

Source: Quantitative Aptitude CAT (Arun Sharma)

13spades + 4 kings + 4 Queens => 21/52.
hence A!

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Ian Stewart: GMAT Instructor; Posts: 2623; Joined: Mon Jun 02, 2008 3:17 amFollowed by: 355 members; Location: Montreal; Thanked: 1090 times; GMAT Score:780

by Ian Stewart » Thu Sep 08, 2011 4:27 pm

You don't need to know anything about cards for the GMAT, but there are 13 spades in a deck, including the K and Q of spades. There are 3 other (non-spade) Queens and 3 other Kings, for a total of 19 cards which are spades, kings or queens. So the answer is 19/52 (you need to be careful here not to double-count the king and queen of spades).

For online GMAT math tutoring, or to buy my higher-level Quant books and problem sets, contact me at ianstewartgmat at gmail.com

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n@resh: Senior | Next Rank: 100 Posts; Posts: 61; Joined: Tue Apr 13, 2010 3:29 am; Thanked: 8 times

by n@resh » Thu Sep 08, 2011 8:36 pm

Ian Stewart wrote:You don't need to know anything about cards for the GMAT, but there are 13 spades in a deck, including the K and Q of spades. There are 3 other (non-spade) Queens and 3 other Kings, for a total of 19 cards which are spades, kings or queens. So the answer is 19/52 (you need to be careful here not to double-count the king and queen of spades).

Oh, yeap..i messup...spade consists a king and queen.

Thank you.

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ikaplan: Master | Next Rank: 500 Posts; Posts: 181; Joined: Fri Sep 04, 2009 12:06 pmFollowed by: 1 member; Thanked: 17 times

by ikaplan » Fri Sep 09, 2011 3:16 am

I got 21/52 and my answer was incorrect- that is why I referred to the forum.

Thanks for the hint- I guess such tips will make us more 'trap vigilant' (which is key for success on the GMAT)

"Commitment is more than just wishing for the right conditions. Commitment is working with what you have."

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