
Shortcut Trick
Net discount for two rates a and b = a + b − (a × b / 100).
For 12% and 15%: 12 + 15 − (12 × 15 / 100) = 27 − 1.8 = 25.2%.
For 25.2% and 18%: 25.2 + 18 − (25.2 × 18 / 100) = 43.2 − 4.536 = 38.664%.
∴ The correct answer is 38.664%.

Alternate Method
Given: Successive discounts = 12%, 15%, and 18%
Formula: Final Price = MP × (100 − d1)/100 × (100 − d2)/100 × (100 − d3)/100
MP = 100
−12%
−15%
−18%
Net SP = 61.336
Total Discount = 38.664%
⇒ Let Marked Price (MP) = 100 units
⇒ Price after 1st discount = 100 × (88/100) = 88 units
⇒ Price after 2nd discount = 88 × (85/100) = 74.8 units
⇒ Price after 3rd discount = 74.8 × (82/100) = 61.336 units
⇒ Single equivalent discount = MP − Final Price = 100 − 61.336 = 38.664 units
⇒ Discount percentage = (38.664/100) × 100 = 38.664%
∴ The correct answer is 38.664%.

Additional Information
Successive Discount Property
The order in which successive discounts are applied does not change the final selling price. For example, 10% and 20% give the same net result as 20% and 10%.
Effective Discount Formula
For n discounts d1, d2, ... dn, the effective discount is 1 − [(1 − d1/100)(1 − d2/100)...(1 − dn/100)].
Relation between MP and SP
Selling Price (SP) = Marked Price (MP) − Discount. Always calculate discount percentage on the Marked Price (MP).