
Shortcut Trick
Total Annual Expenditure = (3 × 1100) + (5 × 1000) + (4 × 1200) = Rs. 13100
Total Annual Income = Total Expenditure + Total Savings = 13100 + 1300 = Rs. 14400
Average Monthly Income = Total Income ÷ 12 = 14400 ÷ 12 = Rs. 1200
∴ The correct answer is Rs. 1200.

Alternate Method
Given:
Average expenditure for first 3 months = Rs. 1100 / month
Average expenditure for next 5 months = Rs. 1000 / month
Average expenditure for last 4 months = Rs. 1200 / month
Total annual savings = Rs. 1300
Formula Used:
Total Income = Total Expenditure + Total Savings
Average Monthly Income = Total Annual Income ÷ 12
3 Months
Rs. 3300
5 Months
Rs. 5000
4 Months
Rs. 4800
Savings
Rs. 1300
Total Annual Income = 3300 + 5000 + 4800 + 1300 = Rs. 14400
Average Monthly Income = Rs. 14400 ÷ 12 = Rs. 1200
Calculations:
⇒ Total Expenditure for first 3 months = 3 × 1100 = Rs. 3300
⇒ Total Expenditure for next 5 months = 5 × 1000 = Rs. 5000
⇒ Total Expenditure for last 4 months = 4 × 1200 = Rs. 4800
⇒ Total Annual Expenditure = 3300 + 5000 + 4800 = Rs. 13100
⇒ Total Annual Income = Total Expenditure + Total Savings
⇒ Total Annual Income = 13100 + 1300 = Rs. 14400
⇒ Average Monthly Income = 14400 ÷ 12 = Rs. 1200
∴ The correct answer is Rs. 1200.

Additional Information
Income and Expenditure Relationship
Total Income is always equal to the sum of Total Expenditure and Total Savings calculated over a given specific period.
Weighted Average Concept
When averages are provided for different lengths of time (like varying numbers of months), the combined average is found by dividing the total cumulative sum of all values by the total sum of the specific weights (total 12 months in a year).