rahulvsd wrote:f a, b, c, and d are numbers such that abd > 0 and acd < 0, which of the following must be negative?
(A) abcd
(B) abc^2d
(C) a^2bcd^2
(D) a^3bc^2d^3
(E) a^4b^2c^2d^4
[spoiler]OA: C[/spoiler]
Common to both abd>0 and acd<0 is ad.
Thus, there is only way that one product (abd) can be positive while the other (acd) is negative: b and c must be opposite signs.
Thus, bc<0.
Thus,
C must be negative: a²(bc)d² = positive*negative*positive = negative.
The correct answer is
C.
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