Question

Under the 'Airtel One' postpaid plan, the monthly rental is Rs. 99, and call charges are billed on top of this rent based on the distance slab and the network used. A bill of Rs. 199 in a month is definitely not possible when you make only:

• A. 30 calls to Airtel on STD (500+ km) and 55 local calls in a month
• B. 16 calls to Airtel on STD (15 km) and 76 local calls in a month
• C. 10 STD calls (250 km) each to Airtel, GSM and landline respectively, and 30 local calls in a month
• D. 8, 4 and 7 calls to Airtel, GSM and landline respectively on STD (500+ km), and 55 local calls in a month

Hint:

Subtract the fixed rent from Rs. 199 first, then check which option's cheapest possible call cost still exceeds what remains.

Answer 1

The Correct Option is D

A bill of Rs. 199 needs Rs. 100 of call charges once you remove the fixed Rs. 99 rental. Instead of testing each option for an exact match, check the lowest possible spend for every choice and see if Rs. 100 can ever be reached.

1. Option A (30 Airtel STD 500+ km, 55 local calls): spend is fixed at $30(1.5) + 55(1) = 45 + 55 = 100$, so Rs. 100 is reachable and this bill is possible.
2. Option B (16 Airtel STD, 76 local calls): spend is fixed at $16(1.5) + 76(1) = 24 + 76 = 100$, again exactly Rs. 100, so this bill is possible.
3. Option C (10 STD each to Airtel, GSM, landline at 250 km, 30 local calls): the STD part is fixed at $15 + 25 + 25 = 65$, and the local part swings from 30 to 60 depending on the operator mix, so total spend can be anywhere from 95 to 125. Since 100 falls inside 95 to 125, this bill is possible.
4. Option D (8 Airtel, 4 GSM, 7 landline STD at 500+ km, 55 local calls): the STD part is fixed at $12 + 12 + 24.5 = 48.5$, and the local part swings from 55 to 110, so the lowest total spend is $48.5 + 55 = 103.5$.

Every other option can land on exactly Rs. 100, but option D cannot go below Rs. 103.5, so it can never produce a Rs. 199 bill.

Let's summarize:

• Subtract the Rs. 99 rental first to find the target variable spend of Rs. 100.
• Options A, B and C can all reach Rs. 100 either exactly or within their possible range.
• Option D's cheapest possible combination already costs Rs. 103.5, so Rs. 100 is out of reach.

So the bill of Rs. 199 is definitely not possible in option D.