(1000^2 - 999^2) / (101^2 - 99^2)

[aaa]

(1001^2 - 999^2) / (101^2 - 99^2)

10
20
40
80
100

What is the best way to solve this problem? Thanks.

(edited by ron) the correct answer to this question is (a), 10; the original poster had erroneously posted that the correct answer was (c), 40.

[divya]

you can use the formula:

a^2 - b^2 = (a-b)(a+b)

Thus with the given question :

(1001^2 - 999^2)/( 101^2 - 99^2 ) can be written as:

(1001+999)(1001-999)/(101+99)(101-99)

= (2000 * 2)/( 200 * 2)

= 10

Are you sure the answer is 40 and not 10 ? can you please doublecheck

[Guest]

yeah me too getting 10.

[RonPurewal]

http://www.manhattangmat.com/forums/wei ... t2573.html

the answer is 10, not 40.

i have edited the original post so as to minimize potential confusion.