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There are 5 pairs of socks: 2 blue, 2 white, 2 black, 2 yell [#permalink]
27 May 2010, 02:41

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Difficulty:

5% (low)

Question Stats:

37% (04:09) correct
62% (02:12) wrong based on 8 sessions

There are 5 pairs of socks: 2 blue, 2 white, 2 black, 2 yellow, 2 green. You select randomly four socks together. What is the probability that you'll get at least two of the same color?

Re: Probability question: 10 socks [#permalink]
27 May 2010, 03:59

1

This post received KUDOS

Expert's post

nonameee wrote:

There are 5 pairs of socks: 2 blue, 2 white, 2 black, 2 yellow, 2 green. You select randomly four socks together. What is the probability that you'll get at least two of the same color?

"Probability that you'll get at least two of the same color" - means at least one pair (one pair or two pairs out of 4 socks).

P(at least one pair)=1-P(no pair) --> no pair means all socks must be of different colors --> P=1-\frac{C^4_5*2^4}{C^4_{10}}=\frac{13}{21}.

C^4_5 - # of ways to choose 4 different colors out of 5, basically # of ways to choose which 4 color socks will give us one sock (in this case we obviously will have 4 different colors); 2^4 - each of 4 chosen colors can give left or right sock; C^4_{10} - total # of ways to choose 4 socks out of 10.

What solution was given in the book for 41/42?
_________________

Re: Probability question: 10 socks [#permalink]
28 May 2010, 20:26

Thanks for the explanation.

Bunuel wrote:

nonameee wrote:

There are 5 pairs of socks: 2 blue, 2 white, 2 black, 2 yellow, 2 green. You select randomly four socks together. What is the probability that you'll get at least two of the same color?

"Probability that you'll get at least two of the same color" - means at least one pair (one pair or two pairs out of 4 socks).

P(at least one pair)=1-P(no pair) --> no pair means all socks must be of different colors --> P=1-\frac{C^4_5*2^4}{C^4_10}=\frac{13}{21}.

C^4_5 - # of ways to choose 4 different colors out of 5, basically # of ways to choose which 4 color socks will give us one sock (in this case we obviously will have 4 different colors); 2^4 - each of 4 chosen colors can give left or right sock; C^4_{10} - total # of ways to choose 4 socks out of 10.

Re: Probability question: 10 socks [#permalink]
28 May 2010, 21:07

Bunuel wrote:

nonameee wrote:

There are 5 pairs of socks: 2 blue, 2 white, 2 black, 2 yellow, 2 green. You select randomly four socks together. What is the probability that you'll get at least two of the same color?

"Probability that you'll get at least two of the same color" - means at least one pair (one pair or two pairs out of 4 socks).

P(at least one pair)=1-P(no pair) --> no pair means all socks must be of different colors --> P=1-\frac{C^4_5*2^4}{C^4_10}=\frac{13}{21}.

C^4_5 - # of ways to choose 4 different colors out of 5, basically # of ways to choose which 4 color socks will give us one sock (in this case we obviously will have 4 different colors); 2^4 - each of 4 chosen colors can give left or right sock; C^4_{10} - total # of ways to choose 4 socks out of 10.

What solution was given in the book for 41/42?

wait a sec i dont get it. Why isnt 5 choose 4 C^5_4 ?
_________________

Re: Probability question: 10 socks [#permalink]
06 Mar 2014, 10:37

Bunuel wrote:

nonameee wrote:

There are 5 pairs of socks: 2 blue, 2 white, 2 black, 2 yellow, 2 green. You select randomly four socks together. What is the probability that you'll get at least two of the same color?

"Probability that you'll get at least two of the same color" - means at least one pair (one pair or two pairs out of 4 socks).

P(at least one pair)=1-P(no pair) --> no pair means all socks must be of different colors --> P=1-\frac{C^4_5*2^4}{C^4_10}=\frac{13}{21}.

C^4_5 - # of ways to choose 4 different colors out of 5, basically # of ways to choose which 4 color socks will give us one sock (in this case we obviously will have 4 different colors); 2^4 - each of 4 chosen colors can give left or right sock; C^4_{10} - total # of ways to choose 4 socks out of 10.

What solution was given in the book for 41/42?

May i knw the logic behind this? m not getting the numerator part ..
_________________

Bole So Nehal.. Sat Siri Akal.. Waheguru ji help me to get 700+ score !

Re: Probability question: 10 socks [#permalink]
07 Mar 2014, 00:21

Expert's post

sanjoo wrote:

Bunuel wrote:

nonameee wrote:

There are 5 pairs of socks: 2 blue, 2 white, 2 black, 2 yellow, 2 green. You select randomly four socks together. What is the probability that you'll get at least two of the same color?

"Probability that you'll get at least two of the same color" - means at least one pair (one pair or two pairs out of 4 socks).

P(at least one pair)=1-P(no pair) --> no pair means all socks must be of different colors --> P=1-\frac{C^4_5*2^4}{C^4_10}=\frac{13}{21}.

C^4_5 - # of ways to choose 4 different colors out of 5, basically # of ways to choose which 4 color socks will give us one sock (in this case we obviously will have 4 different colors); 2^4 - each of 4 chosen colors can give left or right sock; C^4_{10} - total # of ways to choose 4 socks out of 10.

What solution was given in the book for 41/42?

May i knw the logic behind this? m not getting the numerator part ..

If 4 out of 5 pairs of socks will give one sock, we won't have a matching pair, we'll have 4 different color socks and this is exactly what we are counting in the numerator.

Re: There are 5 pairs of socks: 2 blue, 2 white, 2 black, 2 yell [#permalink]
08 Mar 2014, 04:02

I solved this one be listing method

Prob of at least getting a pair = 1 -prob(all different at four attempts) = 1-( 1 x 8/9 x 6/8 x 4/7) = 1-8/21= 13/21

a) 1 st attempt = getting any color =1 b) 2nd attempt = not getting the color picked in a). = 8/9 c) 3rd attempt = not getting the two colors above = 6/8 d) not getting any of the four colors above = 4/7