1. triangle and ratios

Given a triangle ABC and a point 'D' divides the side AB such that a triangle ADC is formed & AD/DB=1/3. If the area of the triangle ABC is r, then find the area of the triangle ADC in terms of r?

2. let AB = b be the base of triangle ABC and h = height from C to AB ...

area of triangle ABC = (1/2)bh = r