GMATPrep - Number properties - PS

Question

OA later...

Could someone explain the fastest way to solve such questions?

MA · Answer

E.
1. c(d+1) is even means atleast one of either c or d+1 is even. nsf.

2. (c+2) (d+4) is even also means at least one is even but dfonot know. either could be even or odd. nsf

togather also insuffcient cuz at least one of eithr c or d could be even but we do not know which one.

freetheking · Answer

It's C..

S1. c(d+1) = even
e*e
o*e
o*o
insufficient

S2. (c+2)(d+4) = even
e*e
e*o
o*e
insufficient

Combine S1 and S2
c must be even. (since d+1 and d+4 can't be both even or both odd)

ps_dahiya · Answer

C

St1: C(D+1) is even
Cases:
--C---D
1.E---O
2.O---O
3.E---E
So C can be either E(Case 1 and 3) or odd (Case2): INSUFF

St2: (C+2)(D+4) is even
Cases: 
--C---D
1.E---E
2.O---E
3.E---O
So C can be either E(Case 1 and 3) or odd (Case2): INSUFF

Combined:
Case 1 and case 3 of both statements are true. Hence C is always even.:SUFF

bz9 · Answer

Can someone please explain how to set up the second statement? Do you just foil and plug for D?

Thanks in advance

GMATPrep - Number properties - PS

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