Two block averages combined: A car consumes on average 110 litres of petrol per month for the first 7 months and 86 litres per month for the next 5 months. Find the average monthly consumption for the full year.

Difficulty: Easy

Correct Answer: 100 litres

Explanation:

Introduction / Context:
Weighted averages by month counts give the yearly mean consumption.

Given Data / Assumptions:

Concept / Approach:
Compute total litres in each block, add them, then divide by 12 months.

Step-by-Step Solution:

First block total = 7 * 110 = 770Second block total = 5 * 86 = 430Year total = 770 + 430 = 1200Average monthly = 1200 / 12 = 100 litres

Verification / Alternative check:
Proportional weighting by 7 and 5 months is correctly applied.

Why Other Options Are Wrong:

Common Pitfalls:
Taking a simple mean of 110 and 86 without weighting by month counts.

Final Answer:

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