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

 It is currently 29 May 2017, 10:47

### 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 5 blue balls and 7 red balls in the 1st box and 11

Author Message
Intern
Joined: 18 Mar 2005
Posts: 10
Location: kazan
Followers: 0

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

There are 5 blue balls and 7 red balls in the 1st box and 11 [#permalink]

### Show Tags

18 Mar 2005, 12:21
This topic is locked. If you want to discuss this question please re-post it in the respective forum.

There are 5 blue balls and 7 red balls in the 1st box and 11 blue and 4 red in the 2nd one. Ann takes 1 ball out of a box. What is the probability that the chosen ball is blue? (we don't know out of which box Ann's taken the ball)

Don't have OA. Not sure that numbers are correct. Just faced such a question in one of the tests I have taken.
Senior Manager
Joined: 15 Mar 2005
Posts: 418
Location: Phoenix
Followers: 2

Kudos [?]: 27 [0], given: 0

### Show Tags

18 Mar 2005, 14:47
The total probability is

P(getting a blue ball from box 1) x P(choosing the box 1) + P(getting a blue ball from box 2) x P(choosing the box 2)

Since there're two boxes (and assuming the boxes are non biased, and identical), the P(choosing box 1) = P(choosing box 2) = 1/2.

Thus total probability =

1/2 x (5/12) + 1/2 x (11/15) = 1/2 x (69/60) = 69/120.

Hope that helps.
_________________

Who says elephants can't dance?

Intern
Joined: 18 Mar 2005
Posts: 10
Location: kazan
Followers: 0

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

### Show Tags

19 Mar 2005, 12:24
thanks
Intern
Joined: 15 Jun 2005
Posts: 10
Followers: 0

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

### Show Tags

14 Jul 2005, 01:57
Agree with Capslock. Good Explanation.
Senior Manager
Joined: 30 May 2005
Posts: 276
Followers: 1

Kudos [?]: 40 [0], given: 0

### Show Tags

15 Jul 2005, 12:09
inga wrote:
There are 5 blue balls and 7 red balls in the 1st box and 11 blue and 4 red in the 2nd one. Ann takes 1 ball out of a box. What is the probability that the chosen ball is blue? (we don't know out of which box Ann's taken the ball)

Don't have OA. Not sure that numbers are correct. Just faced such a question in one of the tests I have taken.

plz if i am wrong tell me why

the blue marble can be taken either from the first box or the second

prob of a blue first box =5/12

prob of a blue second box 11/15

5/12+11/5 PROB to have a blue one from either box

thanks
Senior Manager
Joined: 04 May 2005
Posts: 279
Location: CA, USA
Followers: 1

Kudos [?]: 57 [0], given: 0

### Show Tags

15 Jul 2005, 17:33
Is the fact that the balls are stored in two seperate boxes affecting the
outcome ? (vs. having them all together)
Intern
Joined: 27 Jun 2005
Posts: 18
Followers: 0

Kudos [?]: 2 [0], given: 0

### Show Tags

16 Jul 2005, 04:07
My first reaction was that the balls should all be treated as if they were stored together instead of in separate containers. I came up with 16/27 this way. However, Kapslock answer also makes sense - I'm just not sure why you need to use the more complicated formula. Can someone explain why 16/27 isn't correct?
16 Jul 2005, 04:07
Display posts from previous: Sort by