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.
Apr 2512:30 AM EDT
-01:30 AM EDT
At one point, she believed GMAT wasn’t for her. After scoring 595, self-doubt crept in and she questioned her potential. But instead of quitting, she made the right strategic changes. The result? A remarkable comeback to 695. Check out how Saakshi did it.
Apr 2601:30 AM EDT
-02:30 AM EDT
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.
Apr 2610:00 AM EDT
-11:00 AM EDT
The Target Test Prep course represents a quantum leap forward in GMAT preparation, a radical reinterpretation of the way that students should study. Try before you buy with a 5-day, full-access trial of the course for FREE!
Apr 2711:00 AM EDT
-12:00 PM EDT
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
Apr 2808:00 AM PDT
-11:00 AM PDT
Whether you are just beginning your MBA journey or fine-tuning your path to a 700+ score, GMAT Day is designed to give you a competitive edge.
May 0111:00 AM PDT
-12:00 PM PDT
Free- full-length test + 15 concept videos + 150+ short videos + study plan!
02 Mar 2013, 09:02
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:
30% (02:00) correct
70%
(01:47)
wrong
based on 204
sessions
History
Date
Time
Result
Not Attempted Yet
A box contains four coins, of which two coins have heads on both their faces, one coin has tail on both its faces and the fourth coin is a normal one. A coin is picked at random and then tossed. If head is the outcome of the toss, then find the probability that the other face (hidden face) of the coin tossed is also a head.
A. 2/5
B. 1/2
C. 4/5
D. 2/3
E. 3/4
A. 2/5
B. 1/2
C. 4/5
D. 2/3
E. 3/4
03 Mar 2013, 05:27
Kudos
Bookmarks
Guys, the question says that a coin is picked at random and then tossed. This means that a coin is picked up from among the four available, and without determining what kind of coin it is, this coin is tossed. The outcome of this toss is heads.
@nt2010: The outcome of the toss (heads), can be obtained in five different ways, so you need to consider each head separately.
@pariearth: What we are trying to do is given that the toss yielded a head, find out if the coin is two-headed or not.
@ConnectTheDots: We are considering just one toss of the coin. The set of outcomes you have described does not come into the picture at all.
Let me try and offer you another explanation. Once we toss one coin at random, we see that the outcome is heads. We are trying to determine if this coin is two-headed. How many ways could we have got this heads by tossing a coin? Five ways, because this could be either of the heads of the two-headed coins, or the one heads on the fair coin. From these five ways, what are the number of ways that this heads would be from a two-headed coin? There are four ways to get heads from a two-headed coin (two from the first two-headed coin and two from the second).
Therefore probability = (number of ways to get heads from a two-headed coin)/(number of ways to get heads from any coin)
= 4/5
@nt2010: The outcome of the toss (heads), can be obtained in five different ways, so you need to consider each head separately.
@pariearth: What we are trying to do is given that the toss yielded a head, find out if the coin is two-headed or not.
@ConnectTheDots: We are considering just one toss of the coin. The set of outcomes you have described does not come into the picture at all.
Let me try and offer you another explanation. Once we toss one coin at random, we see that the outcome is heads. We are trying to determine if this coin is two-headed. How many ways could we have got this heads by tossing a coin? Five ways, because this could be either of the heads of the two-headed coins, or the one heads on the fair coin. From these five ways, what are the number of ways that this heads would be from a two-headed coin? There are four ways to get heads from a two-headed coin (two from the first two-headed coin and two from the second).
Therefore probability = (number of ways to get heads from a two-headed coin)/(number of ways to get heads from any coin)
= 4/5
pariearth
You can use the conditional probability concept here. You need to find the probability that the coin you tossed was a two-heads coin given that you got heads.
P(A given B) = P(A)/P(B)
P(A) = P(Two heads coins) = 2/4 = 1/2 (since 2 of the 4 coins have two heads)
P(B) = P(Getting heads on flipping a coin) = 5/8 (you have 5 heads and 3 tails in total on the 4 coins)
P(A given B) = (1/2)/(5/8) = 4/5
