Proability
This topic has expert replies
- hariharakarthi
- Master | Next Rank: 500 Posts
- Posts: 131
- Joined: Tue Apr 22, 2008 1:54 pm
- Thanked: 3 times
- GMAT Score:550
A certain deck of cards contains 2 blue cards, 2 red cards, 2 yellow cards, and 2 green cards. If two cards are randomly drawn from the deck, what is the probability that they will both are not blue?
Wouldn't the easiest way to approach this problem be to determine the probability that both are blue?
1st card blue = 2/8
2nd card blue = 1/7
2/8 * 1/7 = 1/28 both are blue
1 - 1/28 = 27/28 neither are blue
Whats the OA?
1st card blue = 2/8
2nd card blue = 1/7
2/8 * 1/7 = 1/28 both are blue
1 - 1/28 = 27/28 neither are blue
Whats the OA?
-
- Senior | Next Rank: 100 Posts
- Posts: 59
- Joined: Mon Jul 13, 2009 8:58 pm
- Thanked: 10 times
- GMAT Score:710
If the probability of both being blue is 1/28.
1 - 1/28 = 27/28 will give us the probability that BOTH OF THEM ARE NOT BLUE at the same time. This means that you could have 1 blue and 1 other color...or 2 other colors. So this approach will not work.
1 - 1/28 = 27/28 will give us the probability that BOTH OF THEM ARE NOT BLUE at the same time. This means that you could have 1 blue and 1 other color...or 2 other colors. So this approach will not work.
tom4lax wrote:Wouldn't the easiest way to approach this problem be to determine the probability that both are blue?
1st card blue = 2/8
2nd card blue = 1/7
2/8 * 1/7 = 1/28 both are blue
1 - 1/28 = 27/28 neither are blue
Whats the OA?
Attempt 1: 710, 92% (Q 42, 63%; V 44, 97%)
Attempt 2: Coming soon!
Attempt 2: Coming soon!
-
- Senior | Next Rank: 100 Posts
- Posts: 64
- Joined: Sat Aug 01, 2009 3:13 am
- Thanked: 5 times
- Followed by:1 members
- GMAT Score:740
I think that the case that you are taking is that both are blue. and then subtracting it to get the case when both are not blue. But the question should be interpreted as not even a single card is blue. In this reasoning you are taking cases when 1 is blue and other is not and hence you are getting 27/28tom4lax wrote:Wouldn't the easiest way to approach this problem be to determine the probability that both are blue?
1st card blue = 2/8
2nd card blue = 1/7
2/8 * 1/7 = 1/28 both are blue
1 - 1/28 = 27/28 neither are blue
Whats the OA?
gmat_dest is right in the way he has solved it.. according to me
MS
-
- Senior | Next Rank: 100 Posts
- Posts: 59
- Joined: Mon Jul 13, 2009 8:58 pm
- Thanked: 10 times
- GMAT Score:710
Could you please clarify the last sentence "what is the probability that they will both are not blue?"
Do you mean that they are BOTH not blue
or
Do you mean that NEITHER of them are blue (which means that at most 1 of them can be blue).
Depending on that, the question changes and hence the probability changes.
Thanks.
quote="hariharakarthi"]A certain deck of cards contains 2 blue cards, 2 red cards, 2 yellow cards, and 2 green cards. If two cards are randomly drawn from the deck, what is the probability that they will both are not blue?[/quote]
Do you mean that they are BOTH not blue
or
Do you mean that NEITHER of them are blue (which means that at most 1 of them can be blue).
Depending on that, the question changes and hence the probability changes.
Thanks.
quote="hariharakarthi"]A certain deck of cards contains 2 blue cards, 2 red cards, 2 yellow cards, and 2 green cards. If two cards are randomly drawn from the deck, what is the probability that they will both are not blue?[/quote]
Attempt 1: 710, 92% (Q 42, 63%; V 44, 97%)
Attempt 2: Coming soon!
Attempt 2: Coming soon!