sayak636 wrote:
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?
Thanks.
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:If
a>b and
c>d (signs in same direction:
> and
>) -->
a+c>b+d.
Example:
3<4 and
2<5 -->
3+2<4+5.
You can only apply subtraction when their signs are in the opposite directions:If
a>b and
c<d (signs in opposite direction:
> and
<) -->
a-c>b-d (take the sign of the inequality you subtract from).
Example:
3<4 and
5>1 -->
3-5<4-1.
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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