Bunuel
Is \(p > q\) ?
(1) \(p + r > q + s\) and \(r > s\)
(2) \(p + s < q + r\) and \(s > r\)
Target question: Is p > q? Statement 1: p + r > q + s and r > sImportant: We must resist the temptation to subtract the second inequality from the first inequality (to incorrectly conclude that p > q).
If we have two inequalities in which the inequality symbols are facing the same direction, we can ADD those inequalities, but we can't subtract them.
For more on this, watch the video below. If we take...
p + r > q + s
r > s... and ADD them, we get:
p + 2r > q + 2s There are several values of p, q, r and s that satisfy the inequality
p + 2r > q + 2s. Here are two:
Case a: p = 0, q = 1, r = 10 and s = 0. In this case, the answer to the target question is
NO, p is not greater than qCase b: p = 1, q = 0, r = 10 and s = 0. In this case, the answer to the target question is
YES, p is greater than qSince we can’t answer the
target question with certainty, statement 1 is NOT SUFFICIENT
Statement 2: p + s < q + r and s > r In this case, we have 2 inequalities, BUT the inequality symbols are not facing the same direction, which means we can't add them...YET!Take the inequality
s > r, and multiply both sides by -1 to get:
-s < -r [notice that, since we multiplied both sides of the inequality by a NEGATIVE value, we had to reverse the direction of the inequality symbol]We now have the following two inequalities:
p + s < q + r
-s < -r
Now that the inequality symbols are facing the same direction, we can ADD the inequalities to get:
p > q. Perfect!
Since we can answer the
target question with certainty, statement 2 is SUFFICIENT
Answer: B
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