Given the linear equation y = kx + n, for what values of x will y < 0?
The question asks for what values of x is kx + n < 0?
(1) n = 0. The question becomes: for what values of x is kx < 0? Not sufficient.
(2) k < 0. Not sufficient.
(1)+(2) Since from (2) k < 0, then kx will be negative for x > 0. Sufficient.
I must say that this is a strange question.
There are two kinds of data sufficient questions: YES/NO DS questions and DS questions which ask to find a value.In a Yes/No Data Sufficiency questions, statement is sufficient if the answer is “always yes” or “always no” while a statement is insufficient if the answer is "sometimes yes" and "sometimes no".
When a DS question asks about the value of some variable, then the statement is sufficient ONLY if you can get the single numerical value of this variable.
So, this is not a GMAT type question.
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