Given:
The successive discount are 10% and 20%.
Formula used:
Successive discount = X + Y - (XY)/100
Where,
X = First discount
Y = Second discount
Calculation:
Successive discount =X + Y - (XY)/100
X = 10%, Y = 20%
⇒ 10+ 20 - 200/100
⇒ 28%
∴ The single equivalent discount is 28%.
Alternate Method
Let the MP was Rs100
After first discount, price = 100 – 10 = Rs. 90
After second discount, price = 90 – (90 × 20)/100 = 90 – 18 = Rs. 72
∴ Total single discount = [(100 - 72)/100]× 100 = 28%