mathec wrote:

I just had this one on a practice test and haven't seen it addressed so I thought I'd post a solution that allows one to solve it quickly. Sorry if it's a repeat. The question is:

( 1001^2 - 999^2 ) / (101^2 0 999^2 )

A) 10

B) 20

C) 40

D) 80

E) 100

My Soln:

Expand the stem to:

[(1000 + 1)(1000 + 1) - (1000 - 1)(1000-1)] / [(100+1)(100+1) - (100-1)(100-1)]

the numerator = (1,000)(1,000) + 2,000 + 1 - (1,000)(1,000) + 2,000 - 1

which = 4,000

the denominator = (100)(100) + 200 + 1 - (100)(100) + 200 - 1

which = 400

So 4,000/400 = 10 ANS A

It was discussed many times

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

[(1000 + 1)(1000 + 1) - (1000 - 1)(1000-1)]---the correct formula is

(1001-999)*(1001+999)=2*(2000)IMHO it is much more easier

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IE IMBA 2010