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

Redeem

gmat paper test q

This topic has expert replies
Post new topic Post Reply
Previous Topic Next Topic
Master | Next Rank: 500 Posts
Posts: 109
Joined: Mon Sep 08, 2008 12:47 am

gmat paper test q

by smallsorrow » Sat Sep 20, 2008 1:36 am
There are two flat screens, one with a diagonal of 21 inches and the other one with a diagonal of 19 inches. What is deifference of the areas of the 21 inch screen and the 19 inch screen.

1.2
2.4
3.30
4.35
5.40

I only can come to a solution which a huge calculation. Do you know any efficient way?

OA will follow
Top
Source: — Problem Solving |
Senior | Next Rank: 100 Posts
Posts: 35
Joined: Tue Sep 09, 2008 10:12 pm
Location: Lko
Thanked: 3 times

by manulath » Sat Sep 20, 2008 6:01 am
is the ans 40?
Top

GMAT/MBA Expert

User avatar
GMAT Instructor
Posts: 2623
Joined: Mon Jun 02, 2008 3:17 am
Location: Montreal
Thanked: 1090 times
Followed by:355 members
GMAT Score:780

by Ian Stewart » Sat Sep 20, 2008 6:22 am
I assume the screens are square; otherwise the question is impossible. If the diagonal of a square is x, you can see by using the Pythagorean Theorem that the length of a side of the square is x/sqrt(2), and the area of the square is therefore (x^2)/2. So, in this question we need to find (21^2)/2 - (19^2)/2. I'd find this easiest to calculate using the difference of squares factorization:

21^2/2 - 19^2/2
= (1/2)(21^2 - 19^2)
= (1/2)(21+19)(21-19)
= (1/2)(40)(2)
= 40
For online GMAT math tutoring, or to buy my higher-level Quant books and problem sets, contact me at ianstewartgmat at gmail.com

ianstewartgmat.com
Top
Master | Next Rank: 500 Posts
Posts: 109
Joined: Mon Sep 08, 2008 12:47 am

by smallsorrow » Sat Sep 20, 2008 9:10 am
Hi Ian,

no, the screen is rectangular... as far as I can remember...
... I will look for the original problem tonite and post it..

Thank you.

The OA is 40 btw
Top
User avatar
Legendary Member
Posts: 871
Joined: Wed Aug 13, 2008 7:48 am
Thanked: 48 times

by stop@800 » Sat Sep 20, 2008 9:15 am
Use a^2 - b^2 = (a-b)(a+b)
Top
User avatar
GMAT Instructor
Posts: 3225
Joined: Tue Jan 08, 2008 2:40 pm
Location: Toronto
Thanked: 1710 times
Followed by:614 members
GMAT Score:800

by Stuart@KaplanGMAT » Sat Sep 20, 2008 10:35 am
smallsorrow wrote:Hi Ian,

no, the screen is rectangular... as far as I can remember...
... I will look for the original problem tonite and post it..

Thank you.

The OA is 40 btw
If the screens are not square, there's no way to answer the question from the information given, since you cannot use the diagonal of a rectangle to calcuate the area.

As Ian pointed out, there are two different formulas for the area of a square:

area = side^2

and

area = (diagonal^2)/2

Most people are only familiar with the first formula, but the second is great on questions in which you're given the length of the diagonal instead of the length of a side.
Image

Stuart Kovinsky | Kaplan GMAT Faculty | Toronto

Kaplan Exclusive: The Official Test Day Experience | Ready to Take a Free Practice Test? | Kaplan/Beat the GMAT Member Discount
BTG100 for $100 off a full course
Top
Post new topic Post Reply
• Page 1 of 1