Explanation:

Sol. Ans.(d). All the options are equally good for the customer.

Case 1 –Let the price of the article = 100, after first discount of 10% it will be of 90. After second discount of 20% it will be 90 – 18 (20% of 90) = 72. And after services tax, it will become 72 – 7.2 (10% of 72) = 64.8.

Case 2 Let the price of the article = 100, after first discount of 20% it will be of 80. After second discount of 10% it will be 80 – 8 (10% of 80) = 72. And after services tax, it will become 72 – 7.2 (10% of 72) = = 64.8.

Case 3 Let the price of the article = 100, after 10% service it will be of 90. After second discount of 20% it will be 90 – 18 (20% of 90) = 72. And after the last discount of 10% it will become 72 – 7.2 (10% of 72) = 64.8.