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A box contains 3 pairs of blue socks and 2 pairs of green socks. [#permalink]
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adisaadeks wrote:
Carcass please kindly look into this question, I'm getting B

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yes sir. I will also call GreenlightTestPrep to arms
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Re: A box contains 3 pairs of blue socks and 2 pairs of green socks. [#permalink]
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Let's calculate the opposite probability of NOT getting a matched set and subtract this value from 1.

This could happen only if we pick all three same hand BLUE ; two same hand BLUE and any green ; or two same hand GREEN and any BLUE

BBB: \(\frac{6}{10}*\frac{2}{9}*\frac{1}{8}=\frac{1}{60}\) (after we pick a blue , 6/10, then there is 2 same hand left out of total 9 - 2/9, and so on);

BBG: \((\frac{6}{10}*\frac{2}{9}*\frac{4}{8})*3=\frac{12}{60}\), multiplying by 3 as this scenario can occur in 3 different ways: BBG, BGB, GBB;

GGB: \((\frac{4}{10}*\frac{1}{9}*\frac{6}{8})*3=\frac{6}{60}\);

\(P=1-(\frac{1}{60}+\frac{12}{60}+\frac{6}{60})=\frac{41}{60}\).

The answer should be A in my view
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Re: A box contains 3 pairs of blue socks and 2 pairs of green socks. [#permalink]
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OMG! 😲. This is damn correct, thanks Carcass 👏

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Re: A box contains 3 pairs of blue socks and 2 pairs of green socks. [#permalink]
Carcass, where am I going wrong:

Total ways of choosing 3 socks = 10C3 = 120
Total ways of chosing 1 pair (from 5 pairs) and then 1 other sock = 5C1 * 2 * 8 [choosing 1 pair of 5 and they can be interchanged so *2 and then there are 8 available socks] = 80

Required probability = 80/120 = 2/3 = Qty B --> Answer is C
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Re: A box contains 3 pairs of blue socks and 2 pairs of green socks. [#permalink]
Carcass wrote:
Let's calculate the opposite probability of NOT getting a matched set and subtract this value from 1.

This could happen only if we pick all three same hand BLUE ; two same hand BLUE and any green ; or two same hand GREEN and any BLUE

BBB: \(\frac{6}{10}*\frac{2}{9}*\frac{1}{8}=\frac{1}{60}\) (after we pick a blue , 6/10, then there is 2 same hand left out of total 9 - 2/9, and so on);

BBG: \((\frac{6}{10}*\frac{2}{9}*\frac{4}{8})*3=\frac{12}{60}\), multiplying by 3 as this scenario can occur in 3 different ways: BBG, BGB, GBB;

GGB: \((\frac{4}{10}*\frac{1}{9}*\frac{6}{8})*3=\frac{6}{60}\);

\(P=1-(\frac{1}{60}+\frac{12}{60}+\frac{6}{60})=\frac{41}{60}\).

The answer should be A in my view



Also, in this case you haven't considered GGG ?
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Re: A box contains 3 pairs of blue socks and 2 pairs of green socks. [#permalink]
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Because we calculate the opposite probability of NOT getting a matched set and subtract this value from 1.

This could happen only if we pick all three same hand BLUE gloves; two same hand BLUE gloves and any green glove; or two same hand GREEN gloves and any BLUE glove

:)
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Re: A box contains 3 pairs of blue socks and 2 pairs of green socks. [#permalink]
Carcass wrote:
Because we calculate the opposite probability of NOT getting a matched set and subtract this value from 1.

This could happen only if we pick all three same hand BLUE gloves; two same hand BLUE gloves and any green glove; or two same hand GREEN gloves and any BLUE glove

:)


Oh, thank you sir. But where am I going wrong?


Total ways of choosing 3 socks = 10C3 = 120
Total ways of chosing 1 pair (from 5 pairs) and then 1 other sock = 5C1 * 2 * 8 [choosing 1 pair of 5 and they can be interchanged so *2 and then there are 8 available socks] = 80

Required probability = 80/120 = 2/3 = Qty B --> Answer is C
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Re: A box contains 3 pairs of blue socks and 2 pairs of green socks. [#permalink]
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Try this if it is more helpful

The straight way you want to achieve. NOT always a question must be attacked in ONE way. You must use the most EFFICIENT way

Quote:
Bleft (3), Bright(3), Gleft (2), Gright(2)

Bleft, Bright, G
Get a Bleft and Bright in (3/10)*(3/9) ways. Then get any green in 4/8 ways.
Probability of getting B pair and a G = (3/10)*(3/9)*(4/8)*3!
(You multiply by 3! here because you could pick in some other order e.g. Bright, Bleft, G or Bleft, G, Bright etc)

Bleft, Bright, B
Get a Bleft and Bright in (3/10)*(3/9) ways. Then get any blue in 4/8 ways.
Probability of getting B pair and another B = (3/10)*(3/9)*(4/8)*3!/2!
(You multiply by 3! here to account for the order e.g. Bright, Bleft, Bleft or Bleft, Bright, Bright etc but two gloves will be identical so you divide by 2!)

Gleft, Gright, B
Get a Gleft and Gright in (2/10)*(2/9) ways. Then get any Blue in 6/8 ways.
Probability of getting G pair and a B = (2/10)*(2/9)*(6/8)*3!

Gleft, Gright, G
Get a Gleft and Gright in (2/10)*(2/9) ways. Then get any other G in 2/8 ways.
Probability of getting G pair and a G = (2/10)*(2/9)*(2/8)*3!/2!

Adding them all up, you get 41/60.

Note here that we cannot say that let's get Bleft, Bright and then any one of the remaining gloves. We need to take separate cases for the third glove (B or G i.e. first two cases above) because the number of arrangements of Bleft, Bright, G is different from number of arrangements of Bleft, Bright, B as we see above. In one case we multiply by 3! because all 3 gloves are distinct. In the other case, we multiply by 3!/2! because 2 of the gloves are identical. Same logic can be used for the green pair.
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Re: A box contains 3 pairs of blue socks and 2 pairs of green socks. [#permalink]
I calculated this as follows 10C3 = 120 total ways to pick the socks. Then if I pick a Blue sock, I have 3 matching socks available, so 1x3x8. 8 Because I can pick 8 of the other socks. So total being 24.

If I pick Green first, I have 2 matching socks available, so 1x2x8 = 16. So I am getting 40 total possible outcomes. What is the last outcome? Since you guys are getting 41?

I am getting 40/120 = 1/3

Where am I going wrong?
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Re: A box contains 3 pairs of blue socks and 2 pairs of green socks. [#permalink]
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Please refer to the explanations above. They are pretty neat sir
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