BREAKING: Target Test Prep releases Brand New 2026 On Demand GMAT prep course

Redeem

concepts of sets

This topic has expert replies
Post new topic Post Reply
Previous Topic Next Topic
User avatar
Senior | Next Rank: 100 Posts
Posts: 46
Joined: Fri Aug 19, 2011 12:13 am
Location: Delhi, India
Followed by:1 members

concepts of sets

by romitvsingh » Fri Nov 25, 2011 12:20 am
R is the set of positive odd integers less than 50, and S is the set of the squares of the integer in R, How many element does the intersection R & S contain?

a) none
b) two
c) four
d) five
e) seven

pls explain in detail
Eat, sleep GMAT
Top
Source: — Problem Solving |
Legendary Member
Posts: 966
Joined: Sat Jan 02, 2010 8:06 am
Thanked: 230 times
Followed by:21 members

by shankar.ashwin » Fri Nov 25, 2011 12:25 am
Its easier to list elements of S first

S contains squares of all odd numbers

S - {1,9,25,49,-------} - Squares of 1,3,5 and 7 respectively.

R contains odd numbers < 50 : R - {1,3,5,7,9..,25,... , 49}

Clearly 4 elements intersect. C IMO
Top
User avatar
Master | Next Rank: 500 Posts
Posts: 102
Joined: Thu Jul 21, 2011 2:22 am
Location: Lahore, Pakistan
Thanked: 4 times
Followed by:1 members

by chufus » Fri Nov 25, 2011 12:30 am
R would contain : (1,3,5,7,9,11,...............49)
S would contain : (1,9,25,49, 81.............................2401)

Intersecting Set : (1,9,25,49)

The answer is 4...
Top
User avatar
GMAT Instructor
Posts: 509
Joined: Wed Apr 21, 2010 1:08 pm
Location: Irvine, CA
Thanked: 199 times
Followed by:85 members
GMAT Score:750

by tpr-becky » Fri Nov 25, 2011 6:55 pm
The question is really asking how many odd numbers between 1 and 50 are perfect squares. We know that the numbers in set S will go significantly higher than 50 but set R is constrained by having a max of 50 thus we only have to look at those.

List the squares to 50 (will only be the squares of integers up to 7)
1, 4, 9, 16, 25, 36, 49

Which of these are odd - 1, 9, 25 & 49 thus there are 4 intersections.

Best of Luck
Becky
Master GMAT Instructor
The Princeton Review
Irvine, CA
Top
User avatar
Master | Next Rank: 500 Posts
Posts: 359
Joined: Wed Mar 11, 2009 4:37 am
Location: Kolkata, India
Thanked: 50 times
Followed by:2 members

by Abhishek009 » Sat Nov 26, 2011 9:10 am
romitvsingh wrote:R is the set of positive odd integers less than 50, and S is the set of the squares of the integer in R, How many element does the intersection R & S contain?

a) none
b) two
c) four
d) five
e) seven

pls explain in detail

R is the set of positive odd integers less than 50 & S is the set of the squares of the integer in R

So we need to simply find out the odd positive squares upto 50 , which are as follows...

1 , 9 , 25 ,49
Abhishek
Top
Post new topic Post Reply
• Page 1 of 1