Ajit has a certain average for 9 innings. In the tenth innings, he scores 100 runs thereby increasing his average by 8 runs. His new average is:

Answer: Option C

Let Ajit's average be x for 9 innings. So, Ajit scored 9x run in 9 innings.
In the 10^th inning, he scored 100 runs then average became (x+8). And he scored (x + 8) × 10 runs in 10 innings.
Now,
$$\begin{array}{rl}& \Rightarrow 9x+100=10\times \left(x+8\right)\\ & \text{or},9x+100=10x+80\\ & \text{or},x=100-80\\ & \text{or},x=20\\ & \text{New}\text{average}=\left(x+8\right)\\ & =28\text{runs}\end{array}$$