If a is 60% of b, then what percent of 4a is 5b ?

Answer: Option C

$$\begin{array}{rl}& a=60\%\text{ of }b\\ & \Rightarrow a=\frac{60}{100}b\\ & \Rightarrow b=\frac{5}{3}a\end{array}$$
∴ Required percentage :
$$\begin{array}{rl}& =\left(\frac{5b}{4a}\times 100\right)\%\\ & =\left(5\times \frac{5}{3}a\times \frac{1}{4a}\times 100\right)\%\\ & =\left(\frac{625}{3}\right)\%\end{array}$$