The single discount equal to three consecutive discounts of 10%, 12% and 5% ?

Answer: Option C

Let the marked price Rs. 100
$$\begin{array}{rl}& \text{Final selling price}\\ & \text{ = 100}\times \frac{90}{100}\times \frac{88}{100}\times \frac{95}{100}\\ & \text{ = Rs}\text{. 75}\text{.24 }\\ & \text{Net discount }\\ & \text{ = }\left(100-75.24\right)\\ & \text{ = 24}\text{.76}\%\end{array}$$

Alternate :
Single equivalent discount for 10% and 12%
$$\begin{array}{rl}& =\left(10+12-\frac{10\times 12}{100}\right)\%\\ & =20.8\%\end{array}$$
Single equivalent discount for 20.8% and 5%
$$\begin{array}{rl}& =\left(20.8+5-\frac{20.8\times 5}{100}\right)\%\\ & =24.76\%\end{array}$$