A car runs 18.4 km using 2 ½ liters of petrol. What is the mileage in km per liter (rounded to 2 decimals)?
- (a)7.28
- (b)7.36
- (c)7.44
- (d)7.52
Answer
Why
Correct — B. Mileage = distance ÷ fuel.
Fuel = 2½ litres = 2.5 litres
Mileage = 18.4 ÷ 2.5
= 18.4 × 2⁄5 = 36.8 ÷ 5 = 7.36 km per litre → option (b)
The division is exact, so rounding to 2 decimals changes nothing.
Why the others are wrong
- (a)7.28 — 7.28 × 2.5 = 18.2 km, 0.2 km short of the 18.4 km the car ran.
- (c)7.44 — 7.44 × 2.5 = 18.6 km, 0.2 km more than the 18.4 km in the stem.
- (d)7.52 — 7.52 × 2.5 = 18.8 km, 0.4 km more than the distance covered.
Concept
Mileage is distance per unit of fuel, km ÷ litres. It is a rate, so the distance goes on top.
Dividing by 2½ is the same as multiplying by 2⁄5, which avoids long division: double 18.4 to 36.8, then divide by 5.
The options sit 0.08 apart, and 0.08 × 2.5 = 0.2 km, so multiplying any option back by 2.5 shows at once how far its distance is off.
Key facts
- Mileage = distance ÷ fuel used.
- Dividing by a mixed number: convert it first (2½ = 5⁄2), then multiply by the reciprocal.
- Fuel needed = distance ÷ mileage.
Study next
Common traps
- Dividing fuel by distance: 2.5 ÷ 18.4 ≈ 0.136 is litres per km, the reciprocal rate.
- Dividing by 2 and dropping the ½: 18.4 ÷ 2 = 9.2, which is not an option.
Here the rate is asked directly from one distance and one fuel figure, with 2½ written as a mixed number. Multiplying the chosen option back by 2.5 checks it in one step.
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