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

Let original price = Rs. 100
Price after first discount = Rs. 90
Price after second discount = Rs. (80 x 90)/100 = Rs. 72
Price after third discount = Rs. (60 x 72)/100 = Rs. 43.20
∴ Single equivalent discount = (100 - 43.20) = 56.8%