A discount series of 10%, 20% and 40% is equal to a single discount of _____ ?

Explanation:

Original price = Rs. 100

Price after first discount = Rs. 90

Price after second discount = Rs. (80/100 × 90) = Rs. 72

Price after third discount = Rs. (60/100 × 72) = Rs. 43.20

Single discount = (100 – 43.20) = 56.8%