Check GMAT Club Decision Tracker for the Latest School Decision Releases https://gmatclub.com/AppTrack

 It is currently 24 May 2017, 10:08

### GMAT 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

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

Practice
Pays

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

# Events & Promotions

###### Events & Promotions in June
Open Detailed Calendar

# There are 50 balls. 20 are red, 20 are green, 6 are blue, 4

Author Message
VP
Joined: 10 Jun 2007
Posts: 1443
Followers: 7

Kudos [?]: 285 [0], given: 0

There are 50 balls. 20 are red, 20 are green, 6 are blue, 4 [#permalink]

### Show Tags

30 Aug 2007, 18:24
This topic is locked. If you want to discuss this question please re-post it in the respective forum.

There are 50 balls. 20 are red, 20 are green, 6 are blue, 4 are black. What is the probability of drawing two balls of the same color?
Senior Manager
Joined: 06 Mar 2006
Posts: 492
Followers: 8

Kudos [?]: 199 [0], given: 1

### Show Tags

30 Aug 2007, 19:53
20/50*19/49 + 20/50*19/49 +6/50*5/49 +4/50*3/49
=401/1225

The number is kind of weird. But it should be this concept.
GMAT Club Legend
Joined: 07 Jul 2004
Posts: 5045
Location: Singapore
Followers: 31

Kudos [?]: 376 [0], given: 0

### Show Tags

30 Aug 2007, 19:57
Winning cases: 2 red, 2 green, 2 blue or 2 black

P(Red) and P(Red) = 20/50 * 19/49 = 35/245
P(Green) and P(Green) = 20/50 * 19/49 = 35/245
P(Blue) and P(Blue) = 6/50 * 5/49 = 3/245
P(Black) and P(Black) = 4/50 * 3/49 = 6/1225

Total = 53/175
Director
Joined: 22 Aug 2007
Posts: 567
Followers: 1

Kudos [?]: 56 [0], given: 0

### Show Tags

30 Aug 2007, 20:50
bkk145 wrote:
There are 50 balls. 20 are red, 20 are green, 6 are blue, 4 are black. What is the probability of drawing two balls of the same color?

Agreed with above,

we can also use combination method, should yeild the same result

(2C20+2C20+2C6+2C4)/ 2C50

of course, for these numbers better use method above.
CEO
Joined: 29 Mar 2007
Posts: 2562
Followers: 21

Kudos [?]: 453 [0], given: 0

### Show Tags

30 Aug 2007, 21:04
bkk145 wrote:
There are 50 balls. 20 are red, 20 are green, 6 are blue, 4 are black. What is the probability of drawing two balls of the same color?

You have to calculate all scenarios and then add them together.

Red: 20/50*19/49= 380/2450

Green: 20/50*19/49=380/2450

Blue: 6/50*5/49= 30/2450

Black: 4/50*3/49= 12/2450

801/2450 or 401/1225
Director
Joined: 03 May 2007
Posts: 876
Schools: University of Chicago, Wharton School
Followers: 6

Kudos [?]: 208 [0], given: 7

### Show Tags

30 Aug 2007, 21:31
IrinaOK wrote:
bkk145 wrote:
There are 50 balls. 20 are red, 20 are green, 6 are blue, 4 are black. What is the probability of drawing two balls of the same color?

Agreed with above,

we can also use combination method, should yeild the same result

(2C20+2C20+2C6+2C4)/ 2C50

of course, for these numbers better use method above.

i take this one:

p = (20C2 + 20C2 + 6C2 + 4C2) / 2C50
VP
Joined: 10 Jun 2007
Posts: 1443
Followers: 7

Kudos [?]: 285 [0], given: 0

### Show Tags

31 Aug 2007, 06:29
Thanks so much guys for the help. I think probability will always be my weakness.

This problem was emailed to me with OA=1/3 (which is very close all of your answers), but I agree, the numbers might not be correct.
31 Aug 2007, 06:29
Display posts from previous: Sort by