I2.1 Two cards are drawn at random from a pack and not replaced. Find the probability $\frac{1}{a}$ that both cards are hearts.

I2.2 If there are $b$ ways of choosing 15 people from ' $a$ ' people, find $b$.
I2.3 If $c$ signals can be made with $\frac{b}{2 a}$ flags of different colours by raising at least one of the flags, without considering the arrangement of colours, find $c$.

I2.4 There are $c$ balls in a bag, of which 3 are red. What is the probability of drawing a red ball?