BTGModeratorVI wrote: ↑Sun Jul 19, 2020 1:50 pm
If Polygon X has fewer than 9 sides, how many sides does Polygon X have?
(1) The sum of the interior angles of Polygon X is divisible by 16.
(2) The sum of the interior angles of Polygon X is divisible by 15
Answer:
A
Source: Manhattan prep
Target question: How many sides does Polygon X have?
Given: Polygon X has fewer than 9 sides
Useful rule: The sum of the angles in an n-sided polygon = (n - 2)(180º)
Since the polygon has FEWER than 9 sides, there are are exactly SIX possible cases:
case a: There are 8 sides, in which case the sum of the angles = (8 - 2)(180º) =
6(180º)
case b: There are 7 sides, in which case the sum of the angles = (7 - 2)(180º) =
5(180º)
case c: There are 6 sides, in which case the sum of the angles = (6 - 2)(180º) =
4(180º)
case d: There are 5 sides, in which case the sum of the angles = (5 - 2)(180º) =
3(180º)
case e: There are 4 sides, in which case the sum of the angles = (4 - 2)(180º) =
2(180º)
case f: There are 3 sides, in which case the sum of the angles = (3 - 2)(180º) =
180º
Statement 1: The sum of the interior angles of Polygon X is divisible by 16.
Only case c (6 sides) satisfies this condition.
4(180º) = 720, and 720 is divisible by 16.
Since no other cases satisfy the condition in statement 1, it MUST be the case that
the polygon has 6 sides
Since we can answer the
target question with certainty, statement 1 is SUFFICIENT
Statement 2: The sum of the interior angles of Polygon X is divisible by 15.
Since 180 is divisible by 15, we can be certain that any multiple of 180 is also divisible by 15.
So, cases a through to f all satisfy the condition in statement 2.
In other words,
the polygon have have 8, 7, 6, 5, 4, or 3 sides
Since we cannot answer the
target question with certainty, statement 2 is NOT SUFFICIENT
Answer: A
Cheers,
Brent
