(1) a + b < 0sud21 wrote:Is b<0?
1). a+b<0
2). ab>0
If a = -1, b = -2, then a + b = -3 < 0; here b < 0
If a = -2, b = 1, then a + b = -2 + 1 = -1 < 0; here b > 0
No definite answer; NOT sufficient.
(2) ab > 0 if both a and b are positive OR if both a and b are negative.
If a = 1, b = 2, then ab = 2 > 0; here b > 0
If a = -1, b = -2, then ab = 2 > 0; here b < 0
No definite answer; NOT sufficient.
Combining (1) and (2), a + b < 0 and ab > 0 implies that both a and b should be negative, which implies b < 0; SUFFICIENT.
The correct answer is C.
