Four customers used four different discount coupons for their respective transactions in such a way that nobody used any discount coupon sub-optimally. (A discount coupon is used sub-optimally if using another discount coupon could have resulted in a higher discount for the same transaction.) What was the minimum combined spend (before application of any discount)?

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 nobody used any discount coupon sub-optimally. (A discount coupon is used sub-optimally if using another discount coupon could have resulted in a higher discount for the same transaction.)

We need to find the the minimum combined spend (before applying of any discount)

For that, we starts checking for the minimum amount that needs to be spend.

From the table, we know that we can avail coupon E by spending Rs. 200 so we use this and get flat discount of Rs. 50 and we cannot get more discount by spending this amount.

Next, we check for coupon D(as, it requires 2nd lowest minimum spend)

If we spend Rs. 250 and use coupon D, we get only Rs. 25 as a discount, but if we use coupon E for the same amount, we can get Rs. 50 flat discount. (using a discount sub-optimally) so we have to spend a minimum of Rs. 500 so that we get a discount of Rs.50, but now again, we see that by spending Rs. 500, we can get a better discount by using Coupon B.

So, now we will use coupon B for Rs. 500 spending.

Till now, we have used coupons E and B (we can't use these coupons now, also we cannot use coupon D)

We need to use 4 coupons so using remaining 2 coupons (A and C) by spending a amount of Rs. 1200 and Rs. 600 for coupon A and coupon C respectively.

Hence, the minimum combined spend is 200 + 500 + 1200 + 600 = Rs. 2500

Option B is the correct answer.