Nora will enter a ticket lottery every day until she wins the lottery, after which she will no longer enter. If the probability that she wins the ticket lottery is 0.1 (1/10) on each of the Â…rest three days, what is the probability that she wins on the third day?
(A) 0.001
(B) 0.009
(C) 0.081
(D) 0.729
(E) 0.900
this problem was rated as the challenge in Gmat Hacks, though it doesn't appear difficult
5-Day Free Trial
5-day free, full-access trial TTP
Available with Beat the GMAT members only code
MORE DETAILS
logic cracks the quants...
This topic has expert replies
-
Night reader
- Legendary Member
- Posts: 1337
- Joined: Sat Dec 27, 2008 6:29 pm
- Thanked: 127 times
- Followed by:10 members
My knowledge frontiers came to evolve the GMATPill's methods - the credited study means to boost the Verbal competence. I really like their videos, especially for RC, CR and SC. You do check their study methods at https://www.gmatpill.com
-
jaymw
- Master | Next Rank: 500 Posts
- Posts: 144
- Joined: Sun Aug 29, 2010 9:17 am
- Thanked: 40 times
- Followed by:4 members
- GMAT Score:760
Let's use some logic to solve this.
She only gets to the third day if she didn't win on the first 2 days. We can therefore multiply the probabilities of not winning for the first two days (0.9 x 0.9 = 0.81)
On the third day, she has to win to fulfill the mentioned requirement. Therefore we have to multiply 0.81 with the probability of winning (0.81 x 0.1 = 0.081).
Thus, the answer is C.
She only gets to the third day if she didn't win on the first 2 days. We can therefore multiply the probabilities of not winning for the first two days (0.9 x 0.9 = 0.81)
On the third day, she has to win to fulfill the mentioned requirement. Therefore we have to multiply 0.81 with the probability of winning (0.81 x 0.1 = 0.081).
Thus, the answer is C.
GMAT/MBA Expert
-
Rahul@gurome
- GMAT Instructor
- Posts: 1179
- Joined: Sun Apr 11, 2010 9:07 pm
- Location: Milpitas, CA
- Thanked: 447 times
- Followed by:88 members
If Nora is winning on the third day, it means she is losing on the first two days.
Probability of winning each day is 0.1.
Probability of losing each day is 1-0.1 = 0.9.
So the probability of Nora winning on the third day is 0.9*0.9*0.1 = 0.081.
The correct answer is (C).
Probability of winning each day is 0.1.
Probability of losing each day is 1-0.1 = 0.9.
So the probability of Nora winning on the third day is 0.9*0.9*0.1 = 0.081.
The correct answer is (C).
Rahul Lakhani
Quant Expert
Gurome, Inc.
https://www.GuroMe.com
On MBA sabbatical (at ISB) for 2011-12 - will stay active as time permits
1-800-566-4043 (USA)
+91-99201 32411 (India)
Quant Expert
Gurome, Inc.
https://www.GuroMe.com
On MBA sabbatical (at ISB) for 2011-12 - will stay active as time permits
1-800-566-4043 (USA)
+91-99201 32411 (India)
GMAT/MBA Expert
-
Scott@TargetTestPrep
- GMAT Instructor
- Posts: 7280
- Joined: Sat Apr 25, 2015 10:56 am
- Location: Los Angeles, CA
- Thanked: 43 times
- Followed by:29 members
We are given that Nora's probability of winning the lottery on each of the first 3 days is 0.1; thus, the probability of her not winning on any day is 1 - 0.1 = 0.9. We must determine the probability of her winning on day 3, which means she does not win on day 1 or on day 2.Night reader wrote:Nora will enter a ticket lottery every day until she wins the lottery, after which she will no longer enter. If the probability that she wins the ticket lottery is 0.1 (1/10) on each of the Â…rest three days, what is the probability that she wins on the third day?
(A) 0.001
(B) 0.009
(C) 0.081
(D) 0.729
(E) 0.900
P(winning on day 3) = 0.9 x 0.9 x 0.1 = 0.081.
Answer: C
Scott Woodbury-Stewart
Founder and CEO
[email protected]
See why Target Test Prep is rated 5 out of 5 stars on BEAT the GMAT. Read our reviews
