A 40m long wire is cut into 2pcs. One forms a circle with radius r, and the other piece forms a square. What is the total area of the circle and square?
AND
For all positive integers, [m]=m/2 for all even integers and [m]=3m for all odd integers. What does [9] x [6] equal?
I keep coming up with 81, and am having a hard time understanding what I am missing.
Thanks for the help!!
Two More Tricky Problems for me
This topic has expert replies
-
- Newbie | Next Rank: 10 Posts
- Posts: 5
- Joined: Thu Nov 08, 2012 10:49 am
GMAT/MBA Expert
- Brent@GMATPrepNow
- GMAT Instructor
- Posts: 16207
- Joined: Mon Dec 08, 2008 6:26 pm
- Location: Vancouver, BC
- Thanked: 5254 times
- Followed by:1268 members
- GMAT Score:770
Here's the original question in its entirety:rfshocker2255 wrote:A 40m long wire is cut into 2pcs. One forms a circle with radius r, and the other piece forms a square. What is the total area of the circle and square?
A thin piece of wire 40 meters long is cut into two pieces. One piece is used to form a circle with radius r, and the other is used to form a square. No wire is left over. Which of the following represents the total area, in square meters, of the circular and the square regions in terms of r?
a) (pi)r^2
b) (pi)r^2 + 10
c) (pi)r^2 + (1/4)(pi)^2(r)^2
d) (pi)r^2 + [40 - 2(pi)r]^2
e) (pi)r^2 + [1O - (1/2)(pi)r]^2
Here's the algebraic approach:
Since r is the radius of the circle, the area of the circle will be (pi)r^2.
If r is the radius of the circle, the length of wire used for this circle will equal its circumference which is 2(pi)r
So, the length of wire to be used for the square must equal 40 - 2(pi)r
In other words, the perimeter of the square will be 40 - 2(pi)r
Since squares have 4 equal sides, the length of each side of the square will be [40 - 2(pi)r]/4, which simplifies to be 10 - (pi)r/2
If each side of the square has length 10 - (pi)r/2, the area of the square will be [10 - (pi)r/2]^2
So, the total area will equal (pi)r^2 + [10 - (pi)r/2]^2, which is the same as E
Cheers,
Brent
GMAT/MBA Expert
- Brent@GMATPrepNow
- GMAT Instructor
- Posts: 16207
- Joined: Mon Dec 08, 2008 6:26 pm
- Location: Vancouver, BC
- Thanked: 5254 times
- Followed by:1268 members
- GMAT Score:770
You are correct in that [9] x [6] = 81rfshocker2255 wrote: For all positive integers, [m]=m/2 for all even integers and [m]=3m for all odd integers. What does [9] x [6] equal?
I keep coming up with 81, and am having a hard time understanding what I am missing.
9 is odd, so [9] = (3)(9) = 27
6 is even, so [6] = 6/2 = 3
So, [9] x [6] = 27 x 3 = 81
However, the answer choices are as follows:
a) [81]
b) [54]
c) [37]
d) [27]
e) [18]
So, which of these equals 81?
Since 27 is odd, [27] = (3)(27) = 81
So, the correct answer is D
Cheers,
Brent
GMAT/MBA Expert
- Anurag@Gurome
- GMAT Instructor
- Posts: 3835
- Joined: Fri Apr 02, 2010 10:00 pm
- Location: Milpitas, CA
- Thanked: 1854 times
- Followed by:523 members
- GMAT Score:770
Refer to the posts as follows...
For problem 1 >> https://www.beatthegmat.com/geometry-t131113.html#516326
For problem 2 >> https://www.beatthegmat.com/function-pro ... tml#327643
For problem 1 >> https://www.beatthegmat.com/geometry-t131113.html#516326
For problem 2 >> https://www.beatthegmat.com/function-pro ... tml#327643
Anurag Mairal, Ph.D., MBA
GMAT Expert, Admissions and Career Guidance
Gurome, Inc.
1-800-566-4043 (USA)
Join Our Facebook Groups
GMAT with Gurome
https://www.facebook.com/groups/272466352793633/
Admissions with Gurome
https://www.facebook.com/groups/461459690536574/
Career Advising with Gurome
https://www.facebook.com/groups/360435787349781/
GMAT Expert, Admissions and Career Guidance
Gurome, Inc.
1-800-566-4043 (USA)
Join Our Facebook Groups
GMAT with Gurome
https://www.facebook.com/groups/272466352793633/
Admissions with Gurome
https://www.facebook.com/groups/461459690536574/
Career Advising with Gurome
https://www.facebook.com/groups/360435787349781/
- hemant_rajput
- Master | Next Rank: 500 Posts
- Posts: 447
- Joined: Sun Apr 22, 2012 7:13 am
- Thanked: 46 times
- Followed by:13 members
- GMAT Score:700
please post the full question to make it feasible for all the member to answer it.rfshocker2255 wrote:A 40m long wire is cut into 2pcs. One forms a circle with radius r, and the other piece forms a square. What is the total area of the circle and square?
AND
For all positive integers, [m]=m/2 for all even integers and [m]=3m for all odd integers. What does [9] x [6] equal?
I keep coming up with 81, and am having a hard time understanding what I am missing.
Thanks for the help!!
I'm no expert, just trying to work on my skills. If I've made any mistakes please bear with me.