Four customers used four different discount coupons for their respective transactions in such a way that they obtained a total discount of Rs. 710. Which discount coupon was not used?

Tabulating the coupons and the respective minimum & maximum discounts on minimum spend as below-

From the table, we can infer that

Coupon A can be availed only when someone spends a minimum amount of Rs. 1200 and he will obtain a flat discount of Rs. 250.

Coupon B can be availed only when someone spends a minimum amount of Rs. 500 such that he will get a discount of 15% on it which is Rs. 75 and a maximum discount of Rs. 300 can be given when he spends amount greater than or equal to Rs. 2000.

Coupon C can be availed only when someone spends a minimum amount of Rs. 600 and he will obtain a flat discount of Rs. 100.

Coupon D can be availed only when someone spends a minimum amount of Rs. 250 such that he will get a discount of 10% on it which is Rs. 25 and a maximum discount of Rs. 100 can be given when he spends amount greater than or equal to Rs. 1000.

Coupon E can be availed only when someone spends a minimum amount of Rs. 200 and he will obtain a flat discount of Rs. 50.

In this question, it is given that four customers used four different discount coupons for their respective transactions in such a way that they obtained a total discount of Rs. 710.

Let us assume that coupon A was not used, then the four customers can get a maximum discount of (300+100+100+50) = Rs. 550

From the observation, we see that the sum of maximum discounts if all 5 coupons are used is (250+300+100+100+50) = Rs. 800

Therefore, to get a discount of Rs. 710 only one coupon that we can skip is Coupon E because in all other cases, the total discount will be less than Rs. 710

Hence, Option E is the correct answer.