There are 7 non-collinear points. How many triangles can be drawn by joining these points?

Answer: Option A

A triangle is formed by joining any three non-collinear points in pairs.
There are 7 non-collinear points.
The number of triangles formed,
$$\begin{array}{rl}& {=}^7{\text{C}}_3\\ & =\frac{7\times \left(7-1\right)\times \left(7-2\right)}{3!}\\ & =\frac{7\times 6\times 5}{3\times 2\times 1}\\ & =7\times 5\\ & =35\end{array}$$