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

Let original price = Rs. 100
Price after 1 st discount = Rs. 90
Price after 2 nd discount = Rs. (80/100) x 90 = Rs. 72
Price after 3 rd discount = Rs. (60/100) x 72 = Rs. 43.20
∴ Single equivalent discount = (100 - 43.20) = 56.8%