Observe the values of a, b, c given in the table. If we choose numbers a, b and c from rows a, b and c respectively, what is the maximum possible value of $\dfrac{c - b}{a}$?

a	2	4	6	8	10
b	3	5	7	9	11
c	5	10	15	20	25

We get the maximum possible value of $\dfrac{c - b}{a}$, if c is the largest and a, b are the smallest values.

$\Rightarrow \dfrac{c - b}{a} \\[1em] \Rightarrow \dfrac{25 - 3}{2} \\[1em] \Rightarrow \dfrac{22}{2} \\[1em] \Rightarrow 11.$

Hence, the maximum possible value of $\dfrac{c - b}{a}$ = 11.