After getting two successive discounts, a shirt with a list price of Rs.150 is available at Rs. 105. If the value of second discount is 12.5%, what is the value of the first discount?

Correct option is B

​$$\textbf{Given:} \\\text{List Price (L.P.)} = ₹150 \\\text{Final Price} = ₹105 \\\text{Second Discount} = 12.5\% \\\text{Let the first discount be } x\% \\[10pt]\text{After first discount:} \\\text{Price} = 150 \times \left(1 - \frac{x}{100} \right) \\[10pt]\text{After second discount of 12.5\%:} \\ \ \\\text{Final Price} = 150 \times \left(1 - \frac{x}{100} \right) \times \left(1 - \frac{12.5}{100} \right) = 105 \\[10pt] \\ \ \\\Rightarrow 150 \times \left(1 - \frac{x}{100} \right) \times 0.875 = 105 \\ \ \\\Rightarrow 131.25 \times \left(1 - \frac{x}{100} \right) = 105 \\ \ \\ \Rightarrow \left(1 - \frac{x}{100} \right) = \frac{105}{131.25} = 0.8 \\ \ \\\Rightarrow \frac{x}{100} = 1 - 0.8 = 0.2 \\ \ \\\Rightarrow x = 0.2 \times 100 = 20 \\[10pt] \\ {\text{First Discount} = 20\%}$$

Correct answer is (b).