(d) Rs 12500
Let the father’s salary be Rs x. Then,
Part of salary given to the two sons as pocket money =\(\frac{X}{100}\)
Share of the elder son = \(\frac{80}{100}\) x \(\frac{X}{100}\) = \(\frac{4X}{500}\)
Expenditure of the elder son = \(\frac{80}{100}\) x \(\frac{4X}{500}\)
= \(\frac{16X}{2500}\)
\(\therefore\) Savings of the elder son = \(\frac{4X}{500}\)- \(\frac{16X}{2500}\) = \(\frac{4X}{2500}\)
Given, \(\frac{4X}{2500}\) = Rs 20
\(\Rightarrow\) x = Rs \(\frac{20\times 2500}{4}\) =Rs 12500.