Every passenger on a certain airplane is from either Japan or Australia; no one is from both. Every passenger is reading either a novel or a biography; no one is reading both. If a passenger is to be selected at random, is the probability that the passenger is both from Japan and reading a novel greater than the probability that the passenger is both from Australia and reading a biography.
(1) The probability that a randomly selected passenger is either from Japan or reading a novel or both is 208/251.
(2) The probability that a randomly selected passenger is either from Australia or reading a biography or both is 172/251.
DS - Prob. difficult question
This topic has expert replies
- karthikpandian19
- Legendary Member
- Posts: 1665
- Joined: Thu Nov 03, 2011 7:04 pm
- Thanked: 165 times
- Followed by:70 members
Regards,
Karthik
The source of the questions that i post from JUNE 2013 is from KNEWTON
---If you find my post useful, click "Thank"
---
---Never stop until cracking GMAT---
Karthik
The source of the questions that i post from JUNE 2013 is from KNEWTON
---If you find my post useful, click "Thank"
![Smile :)](./images/smilies/smile.png)
![Smile :)](./images/smilies/smile.png)
---Never stop until cracking GMAT---
- eagleeye
- Legendary Member
- Posts: 520
- Joined: Sat Apr 28, 2012 9:12 pm
- Thanked: 339 times
- Followed by:49 members
- GMAT Score:770
Hi karthikpandian19:
This is how I did it:
Let the probability that a person is from Japan be J. Similarly for Australia be A
Let the probability that a person is reading a novel be N. Similarly for Biography be A.
Since no one is from both countries and no one reads both ; we have AJ = 0 ; NB = 0.
Then A+J = 1; N+B =1 (Since P(AuB) = P(A)+P(B)-P(AB)
Now we need to find out whether JN > AB
1) We are given that we select either someone from Japan, or someone who reads a novel or does both.
In other words we need to find J or N or both.
Now we know that:
J = J(N+B) = JN + JB (Note that we could also have arrived at this statement since people from Japan includes both novel readers and biography readers).
similarly, N = N(A+J) = NA + NJ
We are given to find probability of people either from Japan or Novel people or both.
In other words we have JN + JB + NA (note that since Japanese Novel readers are in both sets, we count it only once). We then have JN + JB + NA = 208/251;
Now JN+ JB + NA+ (BA) = J + A = 1
Then, BA = 1 - (JN+JB+NA) = 1-208/251 = 43/251. We don't know what JN is. Hence not sufficient.
2) With similar reasoning as above; we have AB+AN + JB = 172/251 and JN = 1 - (AB + AN + JB) = 1 -172/251 = 79/251; We only know JN from this statement; we don't know AB; Hence not sufficient.
However from both 1 and 2, we have JN = 79/251 and AB = 43/251, Clearly we can see that JN>AB. Hence, C is the correct choice.
Let me know if I got it right, and if this helps![Smile :)](./images/smilies/smile.png)
This is how I did it:
Let the probability that a person is from Japan be J. Similarly for Australia be A
Let the probability that a person is reading a novel be N. Similarly for Biography be A.
Since no one is from both countries and no one reads both ; we have AJ = 0 ; NB = 0.
Then A+J = 1; N+B =1 (Since P(AuB) = P(A)+P(B)-P(AB)
Now we need to find out whether JN > AB
1) We are given that we select either someone from Japan, or someone who reads a novel or does both.
In other words we need to find J or N or both.
Now we know that:
J = J(N+B) = JN + JB (Note that we could also have arrived at this statement since people from Japan includes both novel readers and biography readers).
similarly, N = N(A+J) = NA + NJ
We are given to find probability of people either from Japan or Novel people or both.
In other words we have JN + JB + NA (note that since Japanese Novel readers are in both sets, we count it only once). We then have JN + JB + NA = 208/251;
Now JN+ JB + NA+ (BA) = J + A = 1
Then, BA = 1 - (JN+JB+NA) = 1-208/251 = 43/251. We don't know what JN is. Hence not sufficient.
2) With similar reasoning as above; we have AB+AN + JB = 172/251 and JN = 1 - (AB + AN + JB) = 1 -172/251 = 79/251; We only know JN from this statement; we don't know AB; Hence not sufficient.
However from both 1 and 2, we have JN = 79/251 and AB = 43/251, Clearly we can see that JN>AB. Hence, C is the correct choice.
Let me know if I got it right, and if this helps
![Smile :)](./images/smilies/smile.png)
- aneesh.kg
- Master | Next Rank: 500 Posts
- Posts: 385
- Joined: Mon Apr 16, 2012 8:40 am
- Location: Pune, India
- Thanked: 186 times
- Followed by:29 members
Statement(1):
![Image](https://s17.postimage.org/fjwl3dve3/s_T1.jpg)
Statement(2):
![Image](https://s18.postimage.org/jg6p810r9/St2.jpg)
Combining the two statements,
![Image](https://s14.postimage.org/jhzir1ukt/image.jpg)
[spoiler](C)[/spoiler] is the correct answer.
![Image](https://s17.postimage.org/fjwl3dve3/s_T1.jpg)
Statement(2):
![Image](https://s18.postimage.org/jg6p810r9/St2.jpg)
Combining the two statements,
![Image](https://s14.postimage.org/jhzir1ukt/image.jpg)
[spoiler](C)[/spoiler] is the correct answer.
Aneesh Bangia
GMAT Math Coach
[email protected]
GMATPad:
Facebook Page: https://www.facebook.com/GMATPad
GMAT Math Coach
[email protected]
GMATPad:
Facebook Page: https://www.facebook.com/GMATPad
- karthikpandian19
- Legendary Member
- Posts: 1665
- Joined: Thu Nov 03, 2011 7:04 pm
- Thanked: 165 times
- Followed by:70 members
Here how u r adding BA? can you explain pls???eagleeye wrote:........We then have JN + JB + NA = 208/251;
Now JN+ JB + NA+ (BA) = J + A = 1
Then, BA = 1 - (JN+JB+NA) = 1-208/251 = 43/251. We don't know what JN is. Hence not sufficient.
Regards,
Karthik
The source of the questions that i post from JUNE 2013 is from KNEWTON
---If you find my post useful, click "Thank"
---
---Never stop until cracking GMAT---
Karthik
The source of the questions that i post from JUNE 2013 is from KNEWTON
---If you find my post useful, click "Thank"
![Smile :)](./images/smilies/smile.png)
![Smile :)](./images/smilies/smile.png)
---Never stop until cracking GMAT---