The average expenditure of Chandan in four days is Rs90. If his expenditures for the first three days are Rs100, Rs125 and Rs85 respectively, then what is the expenditure of Chandan for the fourth day?

Answer

To find Chandan's expenditure for the fourth day, we can follow these steps:

### Step 1: Understand the average formula
The average expenditure over four days is given by the formula:
\[ \text{Average} = \frac{\text{Sum of all expenditures}}{\text{Number of days}} \]
In this case, the average expenditure is Rs 90 over 4 days.

### Step 2: Calculate the total expenditure for four days
Using the average, we can calculate the total expenditure for the four days:
\[ \text{Total Expenditure} = \text{Average} \times \text{Number of days} = 90 \times 4 = 360 \]

### Step 3: Sum the expenditures of the first three days
Chandan's expenditures for the first three days are Rs 100, Rs 125, and Rs 85. We need to sum these amounts:
\[ \text{Total Expenditure for first three days} = 100 + 125 + 85 = 310 \]

### Step 4: Set up the equation for the fourth day's expenditure
Let the expenditure for the fourth day be \( X \). The total expenditure for all four days can be expressed as:
\[ \text{Total Expenditure} = \text{Expenditure on Day 1} + \text{Expenditure on Day 2} + \text{Expenditure on Day 3} + \text{Expenditure on Day 4} \]
This gives us the equation:
\[ 360 = 310 + X \]

### Step 5: Solve for \( X \)
To find \( X \), we can rearrange the equation:
\[ X = 360 - 310 = 50 \]

### Conclusion
Chandan's expenditure on the fourth day is Rs 50.

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