Question

what is the single discount equivalent to two successive discounts of 20% and 10% ?

Answer 1

Let the Marked price be Rs.100
Discount 1 = 20% Discount 2= 10%
 Discount1 = 100*20/100 = 20
Hence now the price = 100-20 = 80
Discount 2 = 80*10/100 = 8
Hence the price = 72.
Total discount = 28
Effective discount % = 28/100 * 100 = 28%
OR
Let M.P = 100
S.P = M.P*(100-D1)/100 * (100-D2)/100
        =100*80/100 * 90/100 = 72
Effective discount = 100-72 = 28
Effective discount % =  discount/M.P *100 =28/100 * 100 = 28%

Hope it helps.