To solve the problem step-by-step, we will use the formula for the sum of an arithmetic progression (AP). Here’s how we can approach the solution:
### Step 1: Identify the parameters of the problem
- **Total amount borrowed (S)**: Rs 3,25,000
- **First month's payment (A)**: Rs 30,500
- **Decrease in payment each month (D)**: Rs 1,500
### Step 2: Write the formula for the sum of the first n terms of an AP
The sum of the first n terms (S_n) of an arithmetic progression can be calculated using the formula:
\[ S_n = \frac{n}{2} \times (2A + (n - 1)D) \]
### Step 3: Set up the equation
We know that Ajay needs to repay a total of Rs 3,25,000, so we can set up the equation:
\[ 3,25,000 = \frac{n}{2} \times (2 \times 30,500 + (n - 1)(-1,500)) \]
### Step 4: Simplify the equation
1. Calculate \( 2A \):
\[ 2 \times 30,500 = 61,000 \]
2. Substitute into the equation:
\[ 3,25,000 = \frac{n}{2} \times (61,000 - 1,500(n - 1)) \]
3. Distribute \( -1,500(n - 1) \):
\[ 3,25,000 = \frac{n}{2} \times (61,000 - 1,500n + 1,500) \]
\[ 3,25,000 = \frac{n}{2} \times (62,500 - 1,500n) \]
### Step 5: Multiply both sides by 2 to eliminate the fraction
\[ 6,50,000 = n(62,500 - 1,500n) \]
### Step 6: Rearrange the equation
\[ 6,50,000 = 62,500n - 1,500n^2 \]
Rearranging gives:
\[ 1,500n^2 - 62,500n + 6,50,000 = 0 \]
### Step 7: Simplify the quadratic equation
Divide the entire equation by 100 to simplify:
\[ 15n^2 - 625n + 6500 = 0 \]
### Step 8: Use the quadratic formula to find n
The quadratic formula is given by:
\[ n = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a} \]
Where \( a = 15 \), \( b = -625 \), and \( c = 6500 \).
### Step 9: Calculate the discriminant
1. Calculate \( b^2 - 4ac \):
\[ (-625)^2 - 4 \times 15 \times 6500 \]
\[ 390625 - 390000 = 625 \]
### Step 10: Substitute back into the quadratic formula
\[ n = \frac{625 \pm \sqrt{625}}{30} \]
\[ n = \frac{625 \pm 25}{30} \]
### Step 11: Calculate the two possible values for n
1. First value:
\[ n = \frac{650}{30} = \frac{65}{3} \approx 21.67 \]
2. Second value:
\[ n = \frac{600}{30} = 20 \]
Since n must be a whole number, we take \( n = 20 \).
### Conclusion
Ajay will take **20 months** to clear his borrowed amount.
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