If a car travels 120km on 45 litres of petrol, how much petrol is needed for a journey of 600km?

Analysis

This is a direct proportion problem. Since the car consumes petrol at a constant rate, the ratio of the distance traveled to the petrol consumed remains the same for any distance.

Concept

To solve this, we use the principle of proportionality:

Where:

• Distance$_1$ = 120 km
• Petrol$_1$ = 45 litres
• Distance$_2$ = 600 km
• Petrol$_2$ = $x$ (the unknown amount we need to find)

Step-by-Step Solution

Step 1: Set up the equation.

Step 2: Cross-multiply to solve for $x$.

Step 3: Simplify the calculation.

Step 4: Divide both sides by 120 to isolate $x$.

So, the car needs 225 litres of petrol for a 600 km journey.

Conclusion

The calculation confirms that 225 litres are required.

Correct Option: C

Exam Tip

When dealing with direct proportion questions in JAMB, you can also use the "Unitary Method":

1. Find out how much petrol is needed for just 1 km: $45 \div 120 = 0.375$ litres/km.
2. Multiply that by the new distance: $0.375 \times 600 = 225$ litres. This method is often faster and less prone to errors when you are working under time pressure!