Predict the cost of 100 km

The litre price is only half the journey.

Mix petrol and ethanol, hold the driving-energy target constant, and see how pump price and litres required combine.

Predict equal-price E20
Blend and vehicle
20%
Your pump prices
Run the flow

First blend the energy. Then price the distance.

Blend

E20 means 20% ethanol by volume in this lesson. The blend energy is the volume-weighted component energy.

0.8*100 + 0.2*66.6 = 93.32

Volume

To deliver the same modeled energy, litres move inversely to energy per litre.

6*100/93.32 = 6.4295 L

Cost

Only now multiply litres by pump price. Equal INR/L can still produce unequal INR/100 km.

6.4295*100 = INR 642.95

One model. Two honest outcomes.

Equal pump prices

At INR 100/L for both fuels, the modeled E20 vehicle needs more volume for the same energy target, so cost rises 7.16%.

The counterexample

At INR 90/L, modeled E20 costs INR 578.65 per 100 km. Lower energy does not mean it must always cost more.

The boundary

Real mileage varies by vehicle, calibration, route, driving, weather, and fuel. The indices here are explicit teaching assumptions, not live price or mileage claims.

Set the break-even pump.

Petrol is INR 100/L and the E20 energy index is 93.32. Enter the highest E20 price that keeps modeled cost per 100 km equal.

break-even = petrol price * blend energy / petrol energy

Run the baseline comparison, then solve the transfer.

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