CasperMonday
How many triangles can be formed using 8 points in a given plane?
(1) A triangle is formed by joining 3 distinct points in the plane
(2) Out of 8 given points, three are
collinear Target question: How many triangles can be formed using 8 points in a given plane? Statement 1: A triangle is formed by joining 3 distinct points in the plane STRATEGY: This question highlights an important DS strategy: Always examine both statements before you begin analyzing one of the statements. In doing so, you might pick up on a hint or two about how to solve the question. Without reading statement 2, a student might incorrectly conclude that statement 1 is sufficient, because we can select 3 points out of 8 points in 8C3 ways (i.e.,
56 ways).
HOWEVER, statement 2 reminds us that, if some of those 8 points are
collinear (in a line), then the number of possible triangles we can draw will be
less than 56.
In fact, if all 8 points are collinear, then we can't create
any triangle.
So, if we consider the possibility that some (or even all) of the points are collinear, and
the total number of triangles we can create can range from 0 to 56So, statement 1 is NOT SUFFICIENT
Statement 2: Out of 8 given points, three are collinearHere, we know the exact layout of the eight points: 3 of them are collinear, which means the remaining 5 points are not collinear.
At this point, we COULD start counting all of the possible triangles (but that would be a waste of time, since we need only determine whether this information is sufficient to answer the target question (which it is!)
Since we COULD answer the
target question with certainty, statement 2 is SUFFICIENT
Answer: B
Cheers,
Brent