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. 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.
Author 
Message 
TAGS:

Hide Tags

Manager
Joined: 09 Feb 2013
Posts: 118

A shipment of 250 smartphones contains 84 that are defecti
[#permalink]
Show Tags
22 Mar 2013, 00:07
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
Official Answer and Stats are available only to registered users. Register/ Login.
_________________
Kudos will encourage many others, like me. Good Questions also deserve few KUDOS.



Director
Status: Tutor  BrushMyQuant
Joined: 05 Apr 2011
Posts: 610
Location: India
Concentration: Finance, Marketing
GPA: 3
WE: Information Technology (Computer Software)

Re: A shipment of 250 smartphones contains 84 that are defecti
[#permalink]
Show Tags
22 Mar 2013, 00:14
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
Status: Studying
Joined: 09 Dec 2012
Posts: 26
Location: Russian Federation
Concentration: Finance, Strategy
GMAT Date: 04062013
GPA: 3.6
WE: Consulting (Insurance)

Re: A shipment of 250 smartphones contains 84 that are defecti
[#permalink]
Show Tags
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
Joined: 04 May 2013
Posts: 44

Re: A shipment of 250 smartphones contains 84 that are defecti
[#permalink]
Show Tags
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
Joined: 15 Aug 2011
Posts: 18
Location: United States
Concentration: Marketing, Technology
Schools: HBS '16, Kellogg 1YR '15, Ross '17, Haas EWMBA '15, Tuck '16, Duke '15, Anderson '16, Darden '15, Insead '14, Said'16, Cambridge, ISB '15
GPA: 3.6
WE: Project Management (Computer Software)

Re: A shipment of 250 smartphones contains 84 that are defecti
[#permalink]
Show Tags
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
Joined: 18 Oct 2014
Posts: 855
Location: United States
GPA: 3.98

Re: A shipment of 250 smartphones contains 84 that are defecti
[#permalink]
Show Tags
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
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
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 SelfStudy Course
500+ lessons 3000+ practice problems 800+ HD solutions



Manager
Joined: 24 Sep 2018
Posts: 137

Re: A shipment of 250 smartphones contains 84 that are defecti
[#permalink]
Show Tags
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 kudos, If this post helped you in someway.




Re: A shipment of 250 smartphones contains 84 that are defecti &nbs
[#permalink]
22 Oct 2018, 08:16






