Last visit was: 23 Dec 2024, 02:50 It is currently 23 Dec 2024, 02:50

Close

GRE Prep Club Daily Prep

Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized
for You

we will pick new questions that match your level based on your Timer History

Track
Your Progress

every week, we’ll send you an estimated GRE score based on your performance

Practice
Pays

we will pick new questions that match your level based on your Timer History

Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.

Close

Request Expert Reply

Confirm Cancel
Retired Moderator
Joined: 16 Apr 2020
Status:Founder & Quant Trainer
Affiliations: Prepster Education
Posts: 1546
Own Kudos [?]: 3267 [21]
Given Kudos: 172
Location: India
WE:Education (Education)
Send PM
Senior Manager
Senior Manager
Joined: 03 Dec 2020
Posts: 440
Own Kudos [?]: 61 [0]
Given Kudos: 68
Send PM
avatar
Intern
Intern
Joined: 20 May 2022
Posts: 8
Own Kudos [?]: 4 [1]
Given Kudos: 7
Send PM
Verbal Expert
Joined: 18 Apr 2015
Posts: 30484
Own Kudos [?]: 36825 [0]
Given Kudos: 26100
Send PM
A box contains 3 pairs of blue socks and 2 pairs of green socks. [#permalink]
Expert Reply
adisaadeks wrote:
Carcass please kindly look into this question, I'm getting B

Posted from my mobile device


yes sir. I will also call GreenlightTestPrep to arms
Verbal Expert
Joined: 18 Apr 2015
Posts: 30484
Own Kudos [?]: 36825 [3]
Given Kudos: 26100
Send PM
Re: A box contains 3 pairs of blue socks and 2 pairs of green socks. [#permalink]
2
Expert Reply
1
Bookmarks
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
avatar
Intern
Intern
Joined: 20 May 2022
Posts: 8
Own Kudos [?]: 4 [1]
Given Kudos: 7
Send PM
Re: A box contains 3 pairs of blue socks and 2 pairs of green socks. [#permalink]
1
OMG! 😲. This is damn correct, thanks Carcass 👏

Posted from my mobile device
Manager
Manager
Joined: 23 Sep 2023
Posts: 65
Own Kudos [?]: 15 [0]
Given Kudos: 59
Send PM
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
Manager
Manager
Joined: 23 Sep 2023
Posts: 65
Own Kudos [?]: 15 [0]
Given Kudos: 59
Send PM
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 ?
Verbal Expert
Joined: 18 Apr 2015
Posts: 30484
Own Kudos [?]: 36825 [0]
Given Kudos: 26100
Send PM
Re: A box contains 3 pairs of blue socks and 2 pairs of green socks. [#permalink]
Expert Reply
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

:)
Manager
Manager
Joined: 23 Sep 2023
Posts: 65
Own Kudos [?]: 15 [0]
Given Kudos: 59
Send PM
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
Verbal Expert
Joined: 18 Apr 2015
Posts: 30484
Own Kudos [?]: 36825 [2]
Given Kudos: 26100
Send PM
Re: A box contains 3 pairs of blue socks and 2 pairs of green socks. [#permalink]
1
Expert Reply
1
Bookmarks
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.
Intern
Intern
Joined: 05 Aug 2023
Posts: 4
Own Kudos [?]: 7 [0]
Given Kudos: 5
Send PM
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?
Verbal Expert
Joined: 18 Apr 2015
Posts: 30484
Own Kudos [?]: 36825 [0]
Given Kudos: 26100
Send PM
Re: A box contains 3 pairs of blue socks and 2 pairs of green socks. [#permalink]
Expert Reply
Please refer to the explanations above. They are pretty neat sir
Prep Club for GRE Bot
Re: A box contains 3 pairs of blue socks and 2 pairs of green socks. [#permalink]
Moderators:
GRE Instructor
88 posts
GRE Forum Moderator
37 posts
Moderator
1115 posts
GRE Instructor
234 posts

Powered by phpBB © phpBB Group | Emoji artwork provided by EmojiOne