Sep 27 08:00 PM PDT  09:00 PM PDT Working in collaboration with examPAL we will provide you with a unique online learning experience which will help you reach that higher score. Start your free 7 day trial today. Oct 02 08:00 PM PDT  09:00 PM PDT LEARN WITH AN EXPERT TEACHER—FOR FREE  Take a free practice test, learn content with one of our highestrated teachers, or challenge yourself with a GRE Workshop. Oct 07 07:30 AM PDT  08:30 AM PDT An overview of and discussion about the GRE argument essay. The first 20 minutes of this webinar will consist of a “presentation” on a specific topic, and the last 40 minutes consists of live Q&A covering presubmitted or live questions. Oct 07 09:00 PM PDT  11:00 PM PDT This admissions guide will help you plan your best route to a PhD by helping you choose the best programs your goals, secure strong letters of recommendation, strengthen your candidacy, and apply successfully.
Author 
Message 
TAGS:


VP
Joined: 20 Apr 2016
Posts: 1302
WE: Engineering (Energy and Utilities)
Followers: 22
Kudos [?]:
1312
[1]
, given: 251

A box contains 7 red marbles, 5 blue marbles and 8 green mar [#permalink]
20 Jun 2017, 11:16
1
This post received KUDOS
Question Stats:
79% (01:28) correct
20% (01:46) wrong based on 24 sessions
A box contains 7 red marbles, 5 blue marbles and 8 green marbles. John picks up two marbles at a random from the the bag. What is the probability that John has picked a pair of matching marbles (A) 1/19 (B) 15/90 (C) 7/19 (D) 59/190 (E) 2/190
_________________
If you found this post useful, please let me know by pressing the Kudos Button
Rules for Posting
Got 20 Kudos? You can get Free GRE Prep Club Tests
GRE Prep Club Members of the Month:TOP 10 members of the month with highest kudos receive access to 3 months GRE Prep Club tests
Last edited by pranab223 on 28 Jun 2017, 19:11, edited 2 times in total.




Intern
Joined: 17 Apr 2017
Posts: 7
Followers: 0
Kudos [?]:
8
[2]
, given: 2

Re: A box contains 7 red marbles, 5 blue marbles and 8 green mar [#permalink]
28 Jun 2017, 06:34
2
This post received KUDOS
Probability of picking 2 red marbles = (7/20)*(6/19) Probability of picking 2 blue marbles = (5/20)*(4/19) Probability of picking 2 green marbles = (8/20)*(7/19)
As the above 3 events are mutually exclusive, Probability of picking matching marbles = Probability of picking 2 red marbles + Probability of picking 2 blue marbles + Probability of picking 2 green marbles = (7/20)*(6/19) + (5/20)*(4/19) + (8/20)*(7/19) = 59/190
So, the answer is D



Intern
Joined: 17 Jul 2017
Posts: 15
Followers: 0
Kudos [?]:
7
[0], given: 13

Re: A box contains 7 red marbles, 5 blue marbles and 8 green mar [#permalink]
26 Jul 2017, 01:01
nainy05 wrote: Probability of picking 2 red marbles = (7/20)*(6/19) Probability of picking 2 blue marbles = (5/20)*(4/19) Probability of picking 2 green marbles = (8/20)*(7/19)
As the above 3 events are mutually exclusive, Probability of picking matching marbles = Probability of picking 2 red marbles + Probability of picking 2 blue marbles + Probability of picking 2 green marbles = (7/20)*(6/19) + (5/20)*(4/19) + (8/20)*(7/19) = 59/190
So, the answer is D Hi! I have a question here  why do we consider the denominator of the total base (7+5+8 =20) to be 19? I understand why take 7/20 (total probability. Would require a little more explanation here, thank you!



VP
Joined: 20 Apr 2016
Posts: 1302
WE: Engineering (Energy and Utilities)
Followers: 22
Kudos [?]:
1312
[0], given: 251

Re: A box contains 7 red marbles, 5 blue marbles and 8 green mar [#permalink]
26 Jul 2017, 03:30
nancyjose wrote: nainy05 wrote: Probability of picking 2 red marbles = (7/20)*(6/19) Probability of picking 2 blue marbles = (5/20)*(4/19) Probability of picking 2 green marbles = (8/20)*(7/19)
As the above 3 events are mutually exclusive, Probability of picking matching marbles = Probability of picking 2 red marbles + Probability of picking 2 blue marbles + Probability of picking 2 green marbles = (7/20)*(6/19) + (5/20)*(4/19) + (8/20)*(7/19) = 59/190
So, the answer is D Hi! I have a question here  why do we consider the denominator of the total base (7+5+8 =20) to be 19? I understand why take 7/20 (total probability. Would require a little more explanation here, thank you! Here total no. of marbles is 20 only on first selection, but in the next selection we are left with only 19 marbles instead of 20 so denominator becomes 19. However if we need to take out one more than the denominator will become 18. Since probability = \(\frac{favorable outcome}{total number of outcomes}\) Hope it clears
_________________
If you found this post useful, please let me know by pressing the Kudos Button
Rules for Posting
Got 20 Kudos? You can get Free GRE Prep Club Tests
GRE Prep Club Members of the Month:TOP 10 members of the month with highest kudos receive access to 3 months GRE Prep Club tests



Target Test Prep Representative
Status: Head GRE Instructor
Affiliations: Target Test Prep
Joined: 09 May 2016
Posts: 161
Location: United States
Followers: 8
Kudos [?]:
195
[0], given: 0

Re: A box contains 7 red marbles, 5 blue marbles and 8 green mar [#permalink]
04 May 2018, 09:29
pranab01 wrote: A box contains 7 red marbles, 5 blue marbles and 8 green marbles. John picks up two marbles at a random from the the bag. What is the probability that John has picked a pair of matching marbles
(A) 1/19
(B) 15/90
(C) 7/19
(D) 59/190
(E) 2/190 We have 3 possible scenarios: 1) 2 reds, 2) 2 blues, and 3) 2 greens, thus: Number of ways to select 2 reds is 7C2 = 7!/(2! x 5!) = (7 x 6)/2 = 21. Number of ways to select 2 blues is 5C2 = 5!/(2! x 3!) = (5 x 4)/2! = 10. Number of ways to select 2 greens is 8C2 = 8!/(2! x 6!) = (8 x 7)/2! = 28. Number of ways to select any 2 marbles from 20 is 20C2 = 20!/(2! x 18!) = (20 x 19)/2 = 190. Therefore, P(picking a pair of samecolor marbles) = (21 + 10 + 28)/190 = 59/190. Answer: D
_________________
5star rated online GRE quant self study course See why Target Test Prep is the top rated GRE quant course on GRE Prep Club. Read Our Reviews



Intern
Joined: 21 Nov 2018
Posts: 21
Followers: 0
Kudos [?]:
3
[0], given: 1

Re: A box contains 7 red marbles, 5 blue marbles and 8 green mar [#permalink]
24 Nov 2018, 06:32
Suppose the number of each marble was same. Would you have then taken into consideration the selection of first marble. I am asking because there was a similar question on gumdrops where , the number of different types of gumdrops were same and you had not taken ionto consideration , the probability of picking the first gumdrop and solved the question.



Supreme Moderator
Joined: 01 Nov 2017
Posts: 371
Followers: 10
Kudos [?]:
176
[0], given: 4

Re: A box contains 7 red marbles, 5 blue marbles and 8 green mar [#permalink]
24 Nov 2018, 07:01
kunalkmr62 wrote: Suppose the number of each marble was same. Would you have then taken into consideration the selection of first marble. I am asking because there was a similar question on gumdrops where , the number of different types of gumdrops were same and you had not taken ionto consideration , the probability of picking the first gumdrop and solved the question. Yes.. say this question had 5 of each, then answer would have been .. 1*4/14 it would be same as (5/15)(4/14)+(5/15)(4/14)+(5/15)(4/14)= 1*4/14
_________________
Some useful Theory. 1. Arithmetic and Geometric progressions : https://greprepclub.com/forum/progressionsarithmeticgeometricandharmonic11574.html#p27048 2. Effect of Arithmetic Operations on fraction : https://greprepclub.com/forum/effectsofarithmeticoperationsonfractions11573.html?sid=d570445335a783891cd4d48a17db9825 3. Remainders : https://greprepclub.com/forum/remainderswhatyoushouldknow11524.html 4. Number properties : https://greprepclub.com/forum/numberpropertyallyourequire11518.html 5. Absolute Modulus and Inequalities : https://greprepclub.com/forum/absolutemodulusabetterunderstanding11281.html




Re: A box contains 7 red marbles, 5 blue marbles and 8 green mar
[#permalink]
24 Nov 2018, 07:01





