It is currently 13 Dec 2017, 03:26

# Decision(s) Day!:

CHAT Rooms | Ross R1 | Kellogg R1 | Darden R1 | Tepper R1

### 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
Your Progress

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

# If a light bulb is selected at random from a shipment, what

 new topic post reply Question banks Downloads My Bookmarks Reviews Important topics
Author Message
TAGS:

### Hide Tags

Director
Joined: 01 Apr 2008
Posts: 872

Kudos [?]: 869 [1], given: 18

Name: Ronak Amin
Schools: IIM Lucknow (IPMX) - Class of 2014
If a light bulb is selected at random from a shipment, what [#permalink]

### Show Tags

25 Oct 2009, 04:15
1
This post received
KUDOS
1
This post was
BOOKMARKED
00:00

Difficulty:

15% (low)

Question Stats:

80% (00:28) correct 20% (00:35) wrong based on 131 sessions

### HideShow timer Statistics

If a light bulb is selected at random from a shipment, what is the probability that the light bulb is defective?

(1) The ratio of the number of defective light bulbs to the number of nondefective light bulbs is 1 to 60.

(2) The shipment contains 720 light bulbs.
[Reveal] Spoiler: OA

Last edited by Bunuel on 27 May 2016, 06:59, edited 2 times in total.
Added the OA.

Kudos [?]: 869 [1], given: 18

Senior Manager
Joined: 18 Aug 2009
Posts: 317

Kudos [?]: 355 [0], given: 13

Re: If a light bulb is selected at random from a shipment, what [#permalink]

### Show Tags

25 Oct 2009, 10:01
IMO A.

State 1) Probability = 1/61

State 2) We don't know the number of defective bulbs.

Kudos [?]: 355 [0], given: 13

Intern
Joined: 16 Oct 2010
Posts: 7

Kudos [?]: 1 [0], given: 2

Re: If a light bulb is selected at random from a shipment, what [#permalink]

### Show Tags

17 Oct 2010, 08:03
IMO, the correct answer is C. lets just simply pluggin some numbers. imagine we have a total number of 100 bulbs of which 20 are defective and the rest are none-def. the ratio of def to non-def will be 20 to 80 which is equal to 1 to 4. however if we calculate the probablity based on given info, the probability of ocurring defect in bulbs will be 20 to 100 wich is equal to 1 to 5. as you see, the out come is different. we need to know the total number of light bulbs in order to calculate the probability.

Kudos [?]: 1 [0], given: 2

BSchool Thread Master
Joined: 19 Feb 2010
Posts: 390

Kudos [?]: 205 [0], given: 76

Re: If a light bulb is selected at random from a shipment, what [#permalink]

### Show Tags

17 Oct 2010, 22:12
honeyhani wrote:
IMO, the correct answer is C. lets just simply pluggin some numbers. imagine we have a total number of 100 bulbs of which 20 are defective and the rest are none-def. the ratio of def to non-def will be 20 to 80 which is equal to 1 to 4. however if we calculate the probablity based on given info, the probability of ocurring defect in bulbs will be 20 to 100 wich is equal to 1 to 5. as you see, the out come is different. we need to know the total number of light bulbs in order to calculate the probability.

Well, in the case you proposed, imagine the only information you have is 20/80, or 1/4. Simply calculating 20+80=100 gives you the rate 20/100 or 1/5. And since probability is expressed in ratios or percentages, then 1/5 is already the solution. So you can calculate the total knowing the partial amounts.

In this exercise, with statement 1 you know that the ratio of defective to nondefective is 1/60. That means that defective to total is 1/(1+60), or 1/61. Then statement 1 is sufficient. You don't need to know the actual number of light bulbs, just the rate between defective to nondefective, or defective to total, or nondefective to total.

Kudos [?]: 205 [0], given: 76

Current Student
Joined: 15 Jul 2010
Posts: 246

Kudos [?]: 249 [1], given: 65

GMAT 1: 750 Q49 V42
Re: If a light bulb is selected at random from a shipment, what [#permalink]

### Show Tags

20 Oct 2010, 12:25
1
This post received
KUDOS
A.

1) 1x:60X 1X/61X so 1/61 sufficient
2) insufficient
_________________

Consider KUDOS if my post was helpful.

My Debrief: http://gmatclub.com/forum/750-q49v42-105591.html#p825487

Kudos [?]: 249 [1], given: 65

Intern
Joined: 28 Sep 2010
Posts: 5

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

Re: If a light bulb is selected at random from a shipment, what [#permalink]

### Show Tags

21 Oct 2010, 06:16
can someone please post the OA ? I saw a similar question in a test and the solution said that the total number is needed to find the probability , simply knowing the ratio of one item to the other wouldnt help. Reading the posts above , I am confused . IMO the answer is C. Experts please help.

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

Manager
Joined: 24 Jul 2010
Posts: 91

Kudos [?]: 232 [0], given: 12

Re: If a light bulb is selected at random from a shipment, what [#permalink]

### Show Tags

25 Oct 2010, 09:16
it sounds like the answer is A as we're asked for the probability and not the # of defective light bulbs.

Kudos [?]: 232 [0], given: 12

Director
Joined: 04 Jun 2016
Posts: 645

Kudos [?]: 389 [0], given: 36

GMAT 1: 750 Q49 V43
If a light bulb is selected at random from a shipment, what [#permalink]

### Show Tags

04 Aug 2016, 04:43
Economist wrote:
If a light bulb is selected at random from a shipment, what is the probability that the light bulb is defective?

(1) The ratio of the number of defective light bulbs to the number of nondefective light bulbs is 1 to 60.

(2) The shipment contains 720 light bulbs.

(1) The ratio of the number of defective light bulbs to the number of non-defective light bulbs is 1 to 60.
Defective bulb = x
Non defective bulbs = 60x
Total Bulbs = x+60x=61x
Probablity (Defective Bulb)= $$\frac{Defective}{Total} = \frac{x}{61x} = \frac{1}{61}$$
SUFFICIENT

(2) The shipment contains 720 light bulbs.
We are not given the any info about defective bulbs or good bulbs or any other info in ratio or proportions
INSUFFICIENT

ANSWER IS ONLY A
_________________

Posting an answer without an explanation is "GOD COMPLEX". The world doesn't need any more gods. Please explain you answers properly.
FINAL GOODBYE :- 17th SEPTEMBER 2016. .. 16 March 2017 - I am back but for all purposes please consider me semi-retired.

Kudos [?]: 389 [0], given: 36

Non-Human User
Joined: 09 Sep 2013
Posts: 14877

Kudos [?]: 287 [0], given: 0

Re: If a light bulb is selected at random from a shipment, what [#permalink]

### Show Tags

25 Sep 2017, 22:57
Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email.
_________________

Kudos [?]: 287 [0], given: 0

Re: If a light bulb is selected at random from a shipment, what   [#permalink] 25 Sep 2017, 22:57
Display posts from previous: Sort by

# If a light bulb is selected at random from a shipment, what

 new topic post reply Question banks Downloads My Bookmarks Reviews Important topics

 Powered by phpBB © phpBB Group | Emoji artwork provided by EmojiOne Kindly note that the GMAT® test is a registered trademark of the Graduate Management Admission Council®, and this site has neither been reviewed nor endorsed by GMAC®.