A person speeds 75% of his income. If his income increase by 20% and expenses increase by 15%, his saving will increase by :

Answer: Option D

Let original income = Rs. 100
Then savings = Rs. 25 and expenditure = Rs. 75
New income = Rs. 120
New expenditure :
$$=$$ 115% of Rs. 75
$$\begin{array}{rl}& =\text{Rs}\text{. }\left(\frac{115}{100}\times 75\right)\\ & =\text{Rs}\text{. }\frac{345}{4}\end{array}$$
New saving :
. $$\begin{array}{rl}& =\text{Rs}\text{. }\left(120-\frac{345}{4}\right)\\ & =\text{Rs}\text{. }\frac{135}{4}\end{array}$$
Increase in saving :
$$\begin{array}{rl}& =\text{Rs}\text{. }\left(\frac{135}{4}-25\right)\\ & =\text{Rs}\text{. }\frac{35}{4}\end{array}$$
∴ Percentage increase :
$$\begin{array}{rl}& =\left(\frac{35}{4}\times \frac{1}{25}\times 100\right)\%\\ & =35\%\end{array}$$