Question

Four points lie in the same plane, and each point can act as an endpoint. How many unique line segments can be formed using the set of points?
eight
six
five
four

Answer 1

Call the four points A, B, C, D

Now let's list out all the possible combos of two letters taken at a time (from the four listed above)


AB
AC
AD
BC
BD
CD


So there are 6 unique line segments.


A short cut is to use the formula n*(n-1)/2 where in this case n = 4.