A single discount equivalent to the successive discounts of 10%, 20% and 25% is = ?

Answer: Option C

Let the price is = Rs. 100
After discount price
$$\begin{array}{rl}& \text{ = 100}\times \frac{90}{100}\times \frac{80}{100}\times \frac{75}{100}\\ & \text{ = Rs}\text{. 54}\\ & \text{Difference = 100}-54\\ & =46\%\end{array}$$
So, 46% is a single discount of percent of this series.

Alternate :
Successive discount of 10% of 20%
$$\begin{array}{rl}& =10+20-\frac{10\times 20}{100}\\ & =28\%\end{array}$$
Then successive discount of 28% and 25%
$$\begin{array}{rl}& =28+25-\frac{28\times 25}{100}\\ & =46\%\end{array}$$