Bunuel
Is the average (arithmetic mean) of a and b positive?
(1) a is positive.
(2) b is larger than a.
Target question: Is the average (arithmetic mean) of a and b positive? Statement 1: a is positive. There are several values of a and b that satisfy statement 1. Here are two:
Case a: a = 1 and b = 1, in which case
the average of a and b is 1, which is POSITIVECase b: a = 1 and b = -3, in which case
the average of a and b is -1, which is NEGATIVESince we cannot answer the
target question with certainty, statement 1 is NOT SUFFICIENT
Statement 2: b is larger than a There are several values of a and b that satisfy statement 1. Here are two:
Case a: a = 1 and b = 3, in which case
the average of a and b is 2, which is POSITIVECase b: a = -3 and b = -1, in which case
the average of a and b is -2, which is NEGATIVESince we cannot answer the
target question with certainty, statement 2 is NOT SUFFICIENT
Statements 1 and 2 combined Statement 1 tells us that a is positive
Statement 2 tells us that b is larger than a, which means b is positive.
If a and b are both POSITIVE then
the average of a and b must be POSITIVESince we can answer the
target question with certainty, the combined statements are SUFFICIENT
Answer:
RELATED VIDEO