A person's salary is decreased by steps of 20%, 15% and 10%. Approximately by what percent should the reduced salary be increases so as to get back the original salary ?

Answer: Option D

Let original salary = Rs. 100
New salary :
90% of 85% of 80% of Rs. 100
$$\begin{array}{rl}& =\text{Rs}\text{.}\left(\frac{90}{100}\times \frac{85}{100}\times \frac{80}{100}\times 100\right)\\ & =\text{Rs}\text{.}\frac{306}{5}\end{array}$$
Increase on $$\frac{306}{5}$$ :
= $$\left(100-\frac{306}{5}\right)$$
= $$\frac{194}{5}$$
Increase on 100 :
$$\begin{array}{rl}& =\left(\frac{194}{5}\times \frac{5}{306}\times 100\right)\%\\ & =\frac{9700}{153}\%.\\ & =63.39\approx 63\%\end{array}$$