odd*odd = odd
even*odd = even
even*even = even
c x (d+1) is even => c can be odd or even...
(c+2) x (d+4) is even => c can be odd or even
combine; if d+1 is even, d+4 is odd...if d+1 is odd, d+4 is even..
=> c has to be even...(even*odd = even; even*even = even)
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Is C even?
Source: Beat The GMAT — Data Sufficiency |
A
C * (d+1) is even
means
either
c is even or
d+1 is even that is d is odd
or both
C even || d odd || both
Insuff
B
(c+2) x (d+4) is even
cd is even
c even || d even || both
Insuff
A+B
only common part is c even
hence c has to be even
Answer : C
C * (d+1) is even
means
either
c is even or
d+1 is even that is d is odd
or both
C even || d odd || both
Insuff
B
(c+2) x (d+4) is even
cd is even
c even || d even || both
Insuff
A+B
only common part is c even
hence c has to be even
Answer : C
