It is currently 22 Jun 2017, 05:33

### 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 certain class consists of 8 students, including Don. Each

Author Message
TAGS:

### Hide Tags

Manager
Status: Preparing for GMAT - March 2011
Joined: 21 May 2010
Posts: 148
Location: London
Schools: INSEAD, RSM, HEC, St. Gallen, IF, IESE
WE 1: Finance 6 years
A certain class consists of 8 students, including Don. Each [#permalink]

### Show Tags

01 Mar 2011, 04:39
00:00

Difficulty:

(N/A)

Question Stats:

50% (02:26) correct 50% (00:40) wrong based on 10 sessions

### HideShow timer Statistics

A certain class consists of 8 students, including Don. Each day, three tasks must be completed and are assigned as follows: one of the 8 students is selected at random to complete Task A, one of the remaining 7 students is selected at random to complete Task B, and one of the remaining six students is selected at random to complete Task C. What is the probability that Don will be selected to complete one of the three tasks?

A. 1/3
B. 3/8
C. 1/24
D. 1/336
E. 1/512
[Reveal] Spoiler: OA

_________________

In The World Full Of Duplicates,, I Am The Only Masterpiece..
Girl Power
http://gmatclub.com/forum/beat-the-beast-with-non-native-speaker-108349.html

Math Forum Moderator
Joined: 20 Dec 2010
Posts: 2011
Re: word problem - Probability [#permalink]

### Show Tags

01 Mar 2011, 04:47
$$\frac{1}{8}*1*1 + \frac{7}{8}*\frac{1}{7}*1+\frac{7}{8}*\frac{6}{7}*\frac{1}{6}$$

$$3*\frac{1}{8} = \frac{3}{8}$$

Ans: "B"
_________________
Math Expert
Joined: 02 Sep 2009
Posts: 39576
Re: word problem - Probability [#permalink]

### Show Tags

01 Mar 2011, 06:18
tirupatibalaji wrote:
A certain class consists of 8 students, including Don. Each day, three tasks must be completed and are assigned as follows: one of the 8 students is selected at random to complete Task A, one of the remaining 7 students is selected at random to complete Task B, and one of the remaining six students is selected at random to complete Task C. What is the probability that Don will be selected to complete one of the three tasks?
(A) 1/3
(B) 3/8
(C) 1/24
(D) 1/336
(E) 1/512

Alternately you can find the probability that among 3 students chosen to complete the tasks won't be Don and subtract it from 1:
$$P=1-\frac{C^3_7}{C^3_8}=\frac{3}{8}$$;

The same with probability approach: $$P=1-\frac{7}{8}*\frac{6}{7}*\frac{5}{6}=\frac{3}{8}$$.

_________________
Director
Status: Impossible is not a fact. It's an opinion. It's a dare. Impossible is nothing.
Affiliations: University of Chicago Booth School of Business
Joined: 03 Feb 2011
Posts: 900
Re: word problem - Probability [#permalink]

### Show Tags

01 Mar 2011, 06:21
P(don will not be selected to complete any) = (1 - 1/8) (1 - 1/7) (1 - 1/6) = 5/8

P(don will be selected atleast once) = 1 - 5/8 = 3/8
GMAT Tutor
Joined: 24 Jun 2008
Posts: 1179
Re: word problem - Probability [#permalink]

### Show Tags

01 Mar 2011, 07:14
2
KUDOS
Expert's post
There's no need for a complicated solution here. We're selecting 3 people from 8 and we want to know the probability Don is selected. That's just like lining the 8 people up, and asking the probability Don is one of the first 3 people in line. There are 8 spots for Don, 3 of which are among the first three spots, so the probability must be 3/8.

edit - Or to look at it a different way, each of the 8 people is as likely as anyone else to be selected for A, for B, or for C. That is, the probability Don is selected for A is 1/8, for B is also 1/8 and for C is 1/8, so the probability he is selected for one of the three is 1/8 + 1/8 + 1/8 = 3/8.
_________________

GMAT Tutor in Toronto

If you are looking for online GMAT math tutoring, or if you are interested in buying my advanced Quant books and problem sets, please contact me at ianstewartgmat at gmail.com

Re: word problem - Probability   [#permalink] 01 Mar 2011, 07:14
Similar topics Replies Last post
Similar
Topics:
8 For each student in a certain class, a teacher adjusted the student’s 2 12 Jun 2017, 21:10
9 A certain family consists of 8 adult members, including Susi 9 02 Feb 2017, 12:08
29 A certain class consists of 8 students, including Kim. Each 10 12 Apr 2017, 12:03
24 A certain class consists of 8 students, including Kim 14 24 Aug 2016, 08:51
34 In a certain class consisting of 36 students, some boys and 7 24 Apr 2017, 03:22
Display posts from previous: Sort by