In a bag of balloons, the ratio of red balloons to other : PS Archive
Check GMAT Club Decision Tracker for the Latest School Decision Releases http://gmatclub.com/AppTrack

 It is currently 22 Jan 2017, 04:21

### 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

# In a bag of balloons, the ratio of red balloons to other

Author Message
Senior Manager
Joined: 05 Jun 2008
Posts: 307
Followers: 2

Kudos [?]: 128 [0], given: 0

In a bag of balloons, the ratio of red balloons to other [#permalink]

### Show Tags

15 Oct 2008, 05:47
00:00

Difficulty:

(N/A)

Question Stats:

0% (00:00) correct 0% (00:00) wrong based on 0 sessions

### HideShow timer Statistics

This topic is locked. If you want to discuss this question please re-post it in the respective forum.

In a bag of balloons, the ratio of red balloons to other colours is 1:5, if 3 balloons are selected from the bag at random, what is the probability that (a) at least one balloon is red, (b) exactly one balloon is red?
SVP
Joined: 17 Jun 2008
Posts: 1569
Followers: 11

Kudos [?]: 250 [0], given: 0

### Show Tags

16 Oct 2008, 00:46
Probability of selecting a red baloon is 1/6 and probability of not selecting a red baloon = 5/6.

(a). Probability of at least 1 red baloon
= 1/6*5/6*5/6*3 + 1/6*1/6*5/6*3 + 1/6*1/6*1/6
= 91/216.

(b) Probability of exactly one red baloon
= 1/6*5/6*5/6*3 = 25/72.
Manager
Joined: 15 Apr 2008
Posts: 165
Followers: 2

Kudos [?]: 12 [0], given: 1

### Show Tags

16 Oct 2008, 10:01
scthakur wrote:
Probability of selecting a red baloon is 1/6 and probability of not selecting a red baloon = 5/6.

(a). Probability of at least 1 red baloon
= 1/6*5/6*5/6*3 + 1/6*1/6*5/6*3 + 1/6*1/6*1/6
= 91/216.

(b) Probability of exactly one red baloon
= 1/6*5/6*5/6*3 = 25/72.

i am getting 1/2 as answer
this is how I did it.

total sample space=6C3=20
red balloon can be selected in only 1 way , the other 2 balloons can be selected 5C2=10
so probability of selecting atleast one red balloon is 10/20=1/2

part B of the question is also the same in my opinion, i think it is just worded differently. since there is only one red balloon . the probability of selecting exactly one red balloon will also be the same i.e 1/2

vivek what is the OA
please also keep posting the OA so that we know whether our calculations are right or not.
Senior Manager
Joined: 05 Jun 2008
Posts: 307
Followers: 2

Kudos [?]: 128 [0], given: 0

### Show Tags

17 Oct 2008, 00:36
ALD wrote:
scthakur wrote:
Probability of selecting a red baloon is 1/6 and probability of not selecting a red baloon = 5/6.

(a). Probability of at least 1 red baloon
= 1/6*5/6*5/6*3 + 1/6*1/6*5/6*3 + 1/6*1/6*1/6
= 91/216.

(b) Probability of exactly one red baloon
= 1/6*5/6*5/6*3 = 25/72.

i am getting 1/2 as answer
this is how I did it.

total sample space=6C3=20
red balloon can be selected in only 1 way , the other 2 balloons can be selected 5C2=10
so probability of selecting atleast one red balloon is 10/20=1/2

part B of the question is also the same in my opinion, i think it is just worded differently. since there is only one red balloon . the probability of selecting exactly one red balloon will also be the same i.e 1/2

vivek what is the OA
please also keep posting the OA so that we know whether our calculations are right or not.

Thakur is right OA are
a) Probability of at least 1 red baloon
= 1/6*5/6*5/6*3 + 1/6*1/6*5/6*3 + 1/6*1/6*1/6
= 91/216.

(b) Probability of exactly one red baloon
= 1/6*5/6*5/6*3 = 25/72.
Manager
Joined: 14 Jun 2007
Posts: 170
Location: Vienna, Austria
Followers: 1

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

### Show Tags

18 Oct 2008, 23:17
guys
can someone pls tell me the green part?
(b) Probability of exactly one red baloon
= 1/6*5/6*5/6*3 = 25/72.

i get the 1/6 but not the follwing numbers?!
VP
Joined: 30 Jun 2008
Posts: 1043
Followers: 14

Kudos [?]: 568 [0], given: 1

### Show Tags

18 Oct 2008, 23:45
scthakur wrote:
Probability of selecting a red baloon is 1/6 and probability of not selecting a red baloon = 5/6.

(a). Probability of at least 1 red baloon
= 1/6*5/6*5/6*3 + 1/6*1/6*5/6*3 + 1/6*1/6*1/6
= 91/216.

(b) Probability of exactly one red baloon
= 1/6*5/6*5/6*3 = 25/72.

why are we multiplying 3 here ? Is the order necessary ?
_________________

"You have to find it. No one else can find it for you." - Bjorn Borg

SVP
Joined: 17 Jun 2008
Posts: 1569
Followers: 11

Kudos [?]: 250 [0], given: 0

### Show Tags

19 Oct 2008, 21:04
amitdgr wrote:
scthakur wrote:
Probability of selecting a red baloon is 1/6 and probability of not selecting a red baloon = 5/6.

(a). Probability of at least 1 red baloon
= 1/6*5/6*5/6*3 + 1/6*1/6*5/6*3 + 1/6*1/6*1/6
= 91/216.

(b) Probability of exactly one red baloon
= 1/6*5/6*5/6*3 = 25/72.

why are we multiplying 3 here ? Is the order necessary ?

Yes. The question says "at least one baloon is read"....this means it could be the first baloon, second or the third baloon.
Re: PSP004   [#permalink] 19 Oct 2008, 21:04
Display posts from previous: Sort by