A Single discount equivalent to the series of discounts 20%, 10% and 5% is equal to:

Let Marked price = Rs. $$100$$

After 1st discount of 20%, price = $$100-(\frac{20}{100}\times100)$$

= $$100-20=80$$

After 2nd discount of 10% (on changed price), selling price = $$80-(\frac{10}{100}\times80)$$

= $$80-8=72$$

After 3rd discount of 5% (on changed price), selling price = $$72-(\frac{5}{100}\times72)$$

= $$72-3.6=68.4$$

$$\therefore$$ Net discount % = $$\frac{(100-68.4)}{100}\times100=31.6\%$$

=> Ans - (B)