GMAT Question of the Day - Daily to your Mailbox; hard ones only

It is currently 18 Nov 2018, 02:17

Close

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

Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.

Close

Request Expert Reply

Confirm Cancel
Events & Promotions in November
PrevNext
SuMoTuWeThFrSa
28293031123
45678910
11121314151617
18192021222324
2526272829301
Open Detailed Calendar
  • How to QUICKLY Solve GMAT Questions - GMAT Club Chat

     November 20, 2018

     November 20, 2018

     09:00 AM PST

     10:00 AM PST

    The reward for signing up with the registration form and attending the chat is: 6 free examPAL quizzes to practice your new skills after the chat.
  • The winning strategy for 700+ on the GMAT

     November 20, 2018

     November 20, 2018

     06:00 PM EST

     07:00 PM EST

    What people who reach the high 700's do differently? We're going to share insights, tips and strategies from data we collected on over 50,000 students who used examPAL.

A shipment of 250 smartphones contains 84 that are defecti

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

Hide Tags

Manager
Manager
avatar
Joined: 09 Feb 2013
Posts: 118
A shipment of 250 smartphones contains 84 that are defecti  [#permalink]

Show Tags

New post 22 Mar 2013, 00:07
5
7
00:00
A
B
C
D
E

Difficulty:

  45% (medium)

Question Stats:

68% (01:22) correct 32% (01:21) wrong based on 353 sessions

HideShow timer Statistics

A shipment of 250 smartphones contains 84 that are defective. If a customer buys two smartphones at random from the shipment, what is the approximate probability that both phones are defective?

A. 1/250
B. 1/84
C. 1/11
D. 1/9
E. 1/3

_________________

Kudos will encourage many others, like me.
Good Questions also deserve few KUDOS.

Director
Director
User avatar
G
Status: Tutor - BrushMyQuant
Joined: 05 Apr 2011
Posts: 610
Location: India
Concentration: Finance, Marketing
Schools: XLRI (A)
GMAT 1: 700 Q51 V31
GPA: 3
WE: Information Technology (Computer Software)
Re: A shipment of 250 smartphones contains 84 that are defecti  [#permalink]

Show Tags

New post 22 Mar 2013, 00:14
1
emmak wrote:
A shipment of 250 smartphones contains 84 that are defective. If a customer buys two smartphones at random from the shipment, what is the approximate probability that both phones are defective?
a)\(\frac{1}{250}\)
b)\(\frac{1}{84}\)
c)\(\frac{1}{11}\)
d)\(\frac{1}{9}\)
e)\(\frac{1}{3}\)


Probability of chosing one defective phone from a lot of 250 which ontains 84 defective phones is = (84/250)
Probability of chosing one defective phone from a lot of 249(we already picked one) which ontains 83(we already picked one) defective phones is = (83/249)

Combined probability of series of events = product of the probabilities = (84/250)*(83/249)

84/250 is close to (1/3) and (83/249)= (1/3)
so answer is (1/3)*(1/3) = (1/9)

So, answer will be D
Hope it helps!
_________________

Ankit

Check my Tutoring Site -> Brush My Quant

GMAT Quant Tutor
How to start GMAT preparations?
How to Improve Quant Score?
Gmatclub Topic Tags
Check out my GMAT debrief

How to Solve :
Statistics || Reflection of a line || Remainder Problems || Inequalities

Intern
Intern
avatar
Status: Studying
Joined: 09 Dec 2012
Posts: 26
Location: Russian Federation
Concentration: Finance, Strategy
GMAT Date: 04-06-2013
GPA: 3.6
WE: Consulting (Insurance)
GMAT ToolKit User
Re: A shipment of 250 smartphones contains 84 that are defecti  [#permalink]

Show Tags

New post 08 Jul 2013, 13:43
Amm... this doesn't seem that difficult.

The only problem is quickly identifying that 84 is one third.

Chances of picking 1 defective phone = 84 / 250 = ~0.33 (25/8 is even faster)
Chances of picking 2 phones then = 0.33 x 0.33 = 1/3 x 1/3 = 1/9
If we need to go further = 1/3 x 1/3 x 1/3 = 1/27

Lotto goes on :)))
Intern
Intern
avatar
Joined: 04 May 2013
Posts: 44
Re: A shipment of 250 smartphones contains 84 that are defecti  [#permalink]

Show Tags

New post 08 Jul 2013, 14:48
same as what the other two said.

Probability that the first phone is defective is (84/250) ~ (80*3 = 240). Therefore the approximation is (1/3)
Assuming that the first is a favorable outcome, for the next phone there will only be (83/249). Again, the approximation is ~ (1/3)

Probability of both events happening = (1/3)*(1/3) = 1/9 = D
Intern
Intern
User avatar
Joined: 15 Aug 2011
Posts: 18
Location: United States
Concentration: Marketing, Technology
GPA: 3.6
WE: Project Management (Computer Software)
GMAT ToolKit User Reviews Badge
Re: A shipment of 250 smartphones contains 84 that are defecti  [#permalink]

Show Tags

New post 08 Jul 2013, 20:23
emmak wrote:
A shipment of 250 smartphones contains 84 that are defective. If a customer buys two smartphones at random from the shipment, what is the approximate probability that both phones are defective?

A. 1/250
B. 1/84
C. 1/11
D. 1/9
E. 1/3



\(84C2/250C2 = (84*83)/(250*249)= 14/125 = 1/9\)

Note: This is same as picking 2 red colored cards in random from a deck of 52 cards.....
_________________

"Hit KUDOS if you like my explanation"

Current Student
User avatar
Joined: 18 Oct 2014
Posts: 855
Location: United States
GMAT 1: 660 Q49 V31
GPA: 3.98
GMAT ToolKit User
Re: A shipment of 250 smartphones contains 84 that are defecti  [#permalink]

Show Tags

New post 26 May 2016, 08:06
emmak wrote:
A shipment of 250 smartphones contains 84 that are defective. If a customer buys two smartphones at random from the shipment, what is the approximate probability that both phones are defective?

A. 1/250
B. 1/84
C. 1/11
D. 1/9
E. 1/3


probability of selecting two defective phones= 84/250*83/249= 1/9

D is the answer.
_________________

I welcome critical analysis of my post!! That will help me reach 700+

Target Test Prep Representative
User avatar
G
Status: Head GMAT Instructor
Affiliations: Target Test Prep
Joined: 04 Mar 2011
Posts: 2830
Re: A shipment of 250 smartphones contains 84 that are defecti  [#permalink]

Show Tags

New post 15 May 2018, 15:17
emmak wrote:
A shipment of 250 smartphones contains 84 that are defective. If a customer buys two smartphones at random from the shipment, what is the approximate probability that both phones are defective?

A. 1/250
B. 1/84
C. 1/11
D. 1/9
E. 1/3


The probability of getting two defective smartphones is:

84/250 x 83/249 ≈ 1/3 x 1/3 = 1/9

Answer: D
_________________

Jeffery Miller
Head of GMAT Instruction

GMAT Quant Self-Study Course
500+ lessons 3000+ practice problems 800+ HD solutions

Manager
Manager
avatar
S
Joined: 24 Sep 2018
Posts: 137
CAT Tests
Re: A shipment of 250 smartphones contains 84 that are defecti  [#permalink]

Show Tags

New post 22 Oct 2018, 08:16
Veritas Prep Official Solution:

This is dependent probability, so start by setting up your conditions. The odds that the first phone is defective are 84/250. Assume the customer gets that first defective phone. Now one defective phone has been removed, so the odds that second phone is defective are 83/249, since only 83 defective phones and 249 total phones remain. Now we have 84/250 * 83/249, which looks awful. but remember that the GMAT doesn’t tend to give us random, unworkable numbers: there must be a shortcut. 83/249 simplifies perfectly to 1/3, while 84/250 can be simplified as 42/125. Multiplying these together gives us 42/375. 42 goes into 375 almost exactly nine times, so 42/375 is close to 1/9.
_________________

Please award :thumbup: kudos, If this post helped you in someway. :student_man:

GMAT Club Bot
Re: A shipment of 250 smartphones contains 84 that are defecti &nbs [#permalink] 22 Oct 2018, 08:16
Display posts from previous: Sort by

A shipment of 250 smartphones contains 84 that are defecti

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


Copyright

GMAT Club MBA Forum Home| About| Terms and Conditions and Privacy Policy| GMAT Club Rules| Contact| Sitemap

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®.