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If c and d are positive integers, is c even? (1) c2 - 1 is

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Manager
Joined: 14 Mar 2007
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If c and d are positive integers, is c even? (1) c2 - 1 is [#permalink]

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29 Mar 2007, 06:14
This topic is locked. If you want to discuss this question please re-post it in the respective forum.

2. If c and d are positive integers, is c even?

(1) c2 - 1 is odd.
(2) (c - 3) (d + 2) is odd.
please solve and explain
SVP
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29 Mar 2007, 06:48
(D) for me

c EVEN?

From 1
c^2 - 1 = ODD
<=> (c+1) * (c-1) = ODD

At this point, we should notice that c+1 and c-1 are similar if one is odd, the other must be odd too.

Thus, c+1 and c-1 is ODD and c is EVEN

SUFF.

From 2
(c - 3) * (d + 2) = ODD
=> c - 3 is ODD and d+2 is ODD

Thus, c is EVEN (EVEN - ODD = ODD).

SUFF.
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29 Mar 2007, 09:02
andrehaui wrote:
2. If c and d are positive integers, is c even?

(1) c2 - 1 is odd.
(2) (c - 3) (d + 2) is odd.
please solve and explain

D.

1. c^2 - 1 = odd means c^2 is even. so c is even....... sufficient
2. (c - 3) (d + 2) = odd integer also means (c - 3) and (d + 2) both are odd. then c = even and d is odd........ suffficient.
Re: odd/even   [#permalink] 29 Mar 2007, 09:02
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If c and d are positive integers, is c even? (1) c2 - 1 is

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