A petrol tank contains 200 litres of pure petrol. A dishonest seller repeatedly removes 40 litres from the tank and replaces exactly that 40 litres with kerosene.\nEach time, he sells 40 litres from the tank (which may be pure or mixed), and then refills the tank with 40 litres of kerosene.\nAfter this replacement is done 4 times, what is the total amount of kerosene present in the tank?

Introduction:
This is a repeated replacement (successive dilution) problem. Whenever a fixed fraction of a mixture is removed and replaced with another liquid, the original liquid reduces by the same fraction each time. The key is to track how much pure petrol remains after 4 operations, then subtract from total capacity to get kerosene amount.

Given Data / Assumptions:

• Total tank volume = 200 litres
• Each operation removes = 40 litres of current mixture
• Each operation replaces with = 40 litres of kerosene
• Number of operations = 4

Concept / Approach:
After each operation, the fraction of petrol remaining = (1 - removed/total).\nAfter n operations:\nRemaining petrol = initial petrol * (1 - 40/200)^n.\nThen kerosene = total - remaining petrol.

Step-by-Step Solution:
Removed fraction each time = 40/200 = 0.20Remaining fraction each time = 1 - 0.20 = 0.80Remaining petrol after 4 operations = 200 * (0.80^4)0.80^2 = 0.64, and 0.80^4 = 0.64^2 = 0.4096Remaining petrol = 200 * 0.4096 = 81.92 litresKerosene in tank = 200 - 81.92 = 118.08 litres

Verification / Alternative Check:
If petrol left is 81.92 litres, the rest must be kerosene because only kerosene is added during refilling. Total is fixed at 200 litres, so kerosene = 200 - 81.92 = 118.08 litres. This matches the computed result exactly.

Why Other Options Are Wrong:
81.92 litres: this is the petrol left, not the kerosene.96.00 litres or 104.00 litres: these come from incorrect exponent or wrong fraction removed.None of these: incorrect because 118.08 litres is a valid computed value.

Common Pitfalls:
Assuming 40 litres of pure petrol is sold each time (it is 40 litres of mixture).Subtracting 40 litres each time directly instead of using fraction remaining.Using n = 3 instead of 4 operations due to wording confusion.

Final Answer:
118.08 litres