Question

10 points are given on a plane. How many line segments can be drawn using them?

Answer 1

Answer:

45

Step-by-step explanation:

There are 10 points to choose as "starting points" and 9 points to connect them to so you would think that the answer is 10 * 9 = 90. However, this is incorrect as it is over-counting by a factor of 2. Suppose we have two points A and B. Using this method, 2 of the 90 line segments would be AB and BA but AB and BA are the same line segment. Therefore, the answer is 90 / 2 = 45.