GMAT Math Practice Test #1

Answer B: Let original price=100, Sale price after 1st discount = 100 -20 =80. Second discount = 10% of 80 = 8, Net price = 72. Total discount on original price of 100 = 28. A series discount of 20% and 10% is equivalent to a single discount of 28%

Key takeaway: First discount is given on the original sale price, but second discount is on already discounted price and not on the original sale price.