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.

Thank you for using the timer!
We noticed you are actually not timing your practice. Click the START button first next time you use the timer.
There are many benefits to timing your practice, including:

A shipment of 250 smartphones contains 84 that are defecti [#permalink]
22 Mar 2013, 00:07

2

This post received KUDOS

00:00

A

B

C

D

E

Difficulty:

35% (medium)

Question Stats:

70% (02:25) correct
30% (01:40) wrong based on 92 sessions

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?

Re: A shipment of 250 smartphones contains 84 that are defecti [#permalink]
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! _________________

Re: A shipment of 250 smartphones contains 84 that are defecti [#permalink]
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

Re: A shipment of 250 smartphones contains 84 that are defecti [#permalink]
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

Re: A shipment of 250 smartphones contains 84 that are defecti [#permalink]
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..... _________________

Re: A shipment of 250 smartphones contains 84 that are defecti [#permalink]
28 Jul 2014, 21:21

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. _________________