• Take advantage of our featured Black Friday/Cyber Monday deals

• Take advantage of our featured Black Friday/Cyber Monday deals

## Nova Book

##### This topic has expert replies
Legendary Member
Posts: 512
Joined: 18 Jun 2012
Thanked: 42 times
Followed by:20 members

### Nova Book

by sana.noor » Mon Mar 04, 2013 5:26 am
what is the probability that the sum of two different numbers randomly picked (without replacement) from the set S = {1,2,3,4} is 5
a)1/5
b)3/16
c)1/4
d)1/3
e)1/2

d
explanation: 4.3 = 12 ways to select two numbers
where as 4 ways to select two numbers that sum to 5 (1+4, 4+1, 2+3, 3+2)
4/12 = 1/3
Is their any other way to do this question?

this question is from Nova Gmat math bible...is it a good book for practice? the book is poorly edited but can i use it as a supplement?
Work hard in Silence, Let Success make the noise.

If you found my Post really helpful, then don't forget to click the Thank/follow me button.

### GMAT/MBA Expert

GMAT Instructor
Posts: 3835
Joined: 02 Apr 2010
Location: Milpitas, CA
Thanked: 1854 times
Followed by:523 members
GMAT Score:770
by [email protected] » Mon Mar 04, 2013 5:30 am
sana.noor wrote:Is their any other way to do this question?
The method provided in the book is short and simple enough.
You can try for 1 - [Not getting a sum of 5], but that will lead to a bit more calculation.

Or you can try the following method which is almost same as the book.
Number of ways to select 2 numbers from 4 = 4C2 = 6
Number of ways to select 2 numbers from the set such that there sum is 5 --> {1 and 4} or {2 and 3} = 2

Hence, required probability = 2/6 = 1/3

The correct answer is B.
Anurag Mairal, Ph.D., MBA
GMAT Expert, Admissions and Career Guidance
Gurome, Inc.
1-800-566-4043 (USA)