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.
Aptitude
Average
Difficulty: Easy
Choose an option
Answer
Correct Answer: 100 litres
Explanation
Introduction / Context:Weighted averages by month counts give the yearly mean consumption.Given Data / Assumptions:
- First 7 months average = 110 litres
- Next 5 months average = 86 litres
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 litresVerification / Alternative check:Proportional weighting by 7 and 5 months is correctly applied.Why Other Options Are Wrong:
- 96, 98, 102 litres: Do not equal the exact weighted result.
Common Pitfalls:Taking a simple mean of 110 and 86 without weighting by month counts.Final Answer:
100 litres