Correct Option
Let the total volume of petrol in the tank be 'V' units.
Given that the petrol lasts for 10 days, the original daily consumption rate is V/10 units per day.
If daily consumption increases by 25%, the new daily consumption rate will be:
Original daily consumption × (1 + 0.25) = (V/10) × 1.25 = 1.25V/10 units per day.
To determine how many days the tank-full petrol will last with the new consumption rate, divide the total volume by the new daily consumption rate:
Number of days = V / (1.25V/10) = V × (10 / 1.25V) = 10 / 1.25 = 8 days.
Incorrect Options
Options 1 (5), 2 (6), and 3 (7) are incorrect. The calculation, based on a 25% increase in daily petrol consumption, precisely yields 8 days as the duration for which the tank-full petrol will last. These alternative values do not correspond with the correct mathematical derivation.