Find all School-related info fast with the new School-Specific MBA Forum

 It is currently 03 May 2015, 22:47

### 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

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

# A box contain 20 machine parts, 5 of them standard. A worker

Author Message
TAGS:
Intern
Joined: 08 Jun 2004
Posts: 10
Followers: 0

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

A box contain 20 machine parts, 5 of them standard. A worker [#permalink]  10 Jun 2004, 17:08
A box contain 20 machine parts, 5 of them standard. A worker takes out 3 parts at random. Find the probababilty that at least 1 out of three turns out to be standard.
Manager
Joined: 02 Jun 2004
Posts: 154
Location: san jose,ca
Followers: 3

Kudos [?]: 18 [0], given: 0

all possible ways = 20C3
number of ways to pick all three non-standard = 15C3

P = 1 - (15C3/20C3) = 15*14*13/20*19*18 = 0.6
_________________

GS
No excuses - Need 750!!!

GMAT Club Legend
Joined: 15 Dec 2003
Posts: 4313
Followers: 27

Kudos [?]: 216 [0], given: 0

I concur with the reasoning but answer should be 1 - 91/228 = 137/228
Oh well, that was a very close approximation.
_________________

Best Regards,

Paul

Senior Manager
Joined: 06 Dec 2003
Posts: 366
Location: India
Followers: 1

Kudos [?]: 4 [0], given: 0

Re: A new question [#permalink]  11 Jun 2004, 04:50
Avtar wrote:
A box contain 20 machine parts, 5 of them standard. A worker takes out 3 parts at random. Find the probababilty that at least 1 out of three turns out to be standard.

Atleast one will drive three cases :

Total : 20C3 = 1140
One standard and another 2 non-standard : 5C1 * 15C2 = 525
Two standard and another 1 non-standard : 5C2 * 15C1= 150
All three standard : 5C3 = 10

So answer should be: 685 / 1140 = 137 / 228

Dharmin
Intern
Joined: 26 Jan 2003
Posts: 28
Location: Reality
Followers: 1

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

Re: A new question [#permalink]  11 Jun 2004, 05:23
Avtar wrote:
A box contain 20 machine parts, 5 of them standard. A worker takes out 3 parts at random. Find the probababilty that at least 1 out of three turns out to be standard.

P{1<=x<=3}=1-P{x=0} = 1-(15C3/20C3)= 1 - (15!*3!*17!)/(12!*3!*20!) = 1- 15*14*13/(20*19*18) = 1-91/228 = 137/228
_________________

Manager
Joined: 07 May 2004
Posts: 183
Location: Ukraine, Russia(part-time)
Followers: 2

Kudos [?]: 8 [0], given: 0

Re: A new question [#permalink]  12 Jun 2004, 00:54
Avtar wrote:
A box contain 20 machine parts, 5 of them standard. A worker takes out 3 parts at random. Find the probababilty that at least 1 out of three turns out to be standard.

P(at least 1 is standard) = 1 - P(all are non-standard) = 1 - C[3,15]/C[3,20] = ...
Senior Manager
Joined: 07 Oct 2003
Posts: 358
Location: Manhattan
Followers: 2

Kudos [?]: 7 [0], given: 0

I got the process down, but keep forgetting to do
1- probability of getting an unfavorable outcome

and you know that the ETS will conveniently place the other answer among the choices
Manager
Joined: 07 May 2004
Posts: 183
Location: Ukraine, Russia(part-time)
Followers: 2

Kudos [?]: 8 [0], given: 0

lastochka wrote:
I got the process down, but keep forgetting to do
1- probability of getting an unfavorable outcome

and you know that the ETS will conveniently place the other answer among the choices

Yes, you should be aware of such traps in GMAT...
Similar topics Replies Last post
Similar
Topics:
24 A box contains 10 pairs of shoes (20 shoes in total). If two 18 28 Oct 2009, 00:08
One box contains 30 purple balls and 20 red balls, another 1 25 Aug 2007, 23:35
One box contains 30 purple balls and 20 red balls, another 3 08 Nov 2006, 15:39
A box contains 20 pieces of chocolates, including M, S, P 2 21 Apr 2006, 02:20
a box contains 20 pieces of candies including maroon 5 21 Feb 2006, 16:15
Display posts from previous: Sort by