Events & Promotions
|
|
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
Track
Your Progress
Practice
Pays
Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.
Nov 1912:30 PM EST
-01:30 PM EST
Learn how Keshav, a Chartered Accountant, scored an impressive 705 on GMAT in just 30 days with GMATWhiz's expert guidance. In this video, he shares preparation tips and strategies that worked for him, including the mock, time management, and more
Nov 2007:30 AM PST
-08:30 AM PST
Learn what truly sets the UC Riverside MBA apart and how it helps in your professional growth
Nov 2001:30 PM EST
-02:30 PM IST
Learn how Kamakshi achieved a GMAT 675 with an impressive 96th %ile in Data Insights. Discover the unique methods and exam strategies that helped her excel in DI along with other sections for a balanced and high score.
Nov 2211:00 AM IST
-01:00 PM IST
Do RC/MSR passages scare you? e-GMAT is conducting a masterclass to help you learn – Learn effective reading strategies Tackle difficult RC & MSR with confidence Excel in timed test environment- Nov 23
11:00 AM IST
-01:00 PM IST
Attend this free GMAT Algebra Webinar and learn how to master the most challenging Inequalities and Absolute Value problems with ease. 
Nov 2407:00 PM PST
-08:00 PM PST
Full-length FE mock with insightful analytics, weakness diagnosis, and video explanations!
Nov 2510:00 AM EST
-11:00 AM EST
Prefer video-based learning? The Target Test Prep OnDemand course is a one-of-a-kind video masterclass featuring 400 hours of lecture-style teaching by Scott Woodbury-Stewart, founder of Target Test Prep and one of the most accomplished GMAT instructors.
21 Sep 2020, 05:30
Kudos
Bookmarks
C
Be sure to select an answer first to save it in the Error Log before revealing the correct answer (OA)!
Difficulty:
95%
(hard)
Question Stats:
49% (02:53) correct
51%
(03:05)
wrong
based on 69
sessions
History
Date
Time
Result
Not Attempted Yet
There are three sets of key rings A, B and C, for a house. The first set has five keys, the second has seven and the third has eight, of which only one key in each set opens the door to the store room. A keychain is chose at random followed by a key from the set. What is the probability that the chosen key opens the door and it came from the first key chain?
A. 131/840
B. 7/24
C. 56/131
D. 75/131
E. 17/24
Are You Up For the Challenge: 700 Level Questions
A. 131/840
B. 7/24
C. 56/131
D. 75/131
E. 17/24
Are You Up For the Challenge: 700 Level Questions
21 Sep 2020, 05:47
Kudos
Bookmarks
Prob. of choosing right key from A = 1/3 * 1/5 = 1/15
Prob. of choosing right key from B = 1/7 * 1/3 = 1/21
Prob. of choosing right key from C = 1/8 * 1/3 = 1/24
Total Probability = 1/15 + 1/21 + 1/24 = 131/840. IMO A.
Prob. of choosing right key from B = 1/7 * 1/3 = 1/21
Prob. of choosing right key from C = 1/8 * 1/3 = 1/24
Total Probability = 1/15 + 1/21 + 1/24 = 131/840. IMO A.
21 Sep 2020, 06:38
Kudos
Bookmarks
aritrar4
Hi Aritrar4. The question here is: What is the probability that the key came from the 1st Key Chain given that it opens the door.
By Bayes Theorem, P(A given B) = P(A/B) = \(\frac{P(A \space and \space B)}{P(B)}\)
Therefore P(Key Chain A / Opens) = \(\frac{P(Key \space Chain \space and \space Opens)}{P(Opens)}\)
P(Key Chain A and Opens) = \(\frac{1}{3} * \frac{1}{5} = \frac{1}{15}\)
The probability of P(Opens) = \(\frac{131}{840}\) (As found by you)
Therefore the required probability = \(\frac{\frac{1}{15}}{\frac{131}{840}} = \frac{1 \space * \space 840}{15 \space * \space 131} = \frac{56}{131}\)
Option C
Arun Kumar
