Bunuel... I have a doubt in regard to this question. Is it possible to add or subtract two equations, each with an inequality? Say, for example, if X + Y <= A and Z+ W<=B, then can we say that X-Z+Y-W<=A-B and X+Y+Z+W<=A+B?
If so, then S1 tells us that 7n+5p<=20 and we know that 3n+p<=20/3; if we subtract one from the other, we get 4n+4p<=40/3, or n +p<=10/3. Does this mean that S1 is sufficient?
OA for this question is B and it's correct.
As for your solution, notice that:You can only add inequalities when their signs are in the same direction:
(signs in same direction: >
) --> a+c>b+d
.You can only apply subtraction when their signs are in the opposite directions:
(signs in opposite direction: >
) --> a-c>b-d
(take the sign of the inequality you subtract from).
So, we can not subtract 3n+p<=20/3 from 7n+5p<=20 since the signs are in the same direction.
Hope it helps.
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