Mr.khan invested an amount of TK. 13,900 divided into two different schemes A and B at a simple interest rate of 14% per annum and 11% per annum respectively. If the total amount of simple interest earned in 2 years be Tk. 3,508, what was the amount invested in Scheme B?

To determine the amount invested in Scheme B, we need to solve the problem using the given data:

1. Total amount invested: TK 13,900
2. Simple interest rates:
  - Scheme A: 14% per annum
  - Scheme B: 11% per annum
3. Total simple interest earned in 2 years: TK 3,508

Let's denote:
- The amount invested in Scheme A as \( x \)
- The amount invested in Scheme B as \( 13,900 - x \)

Calculate Simple Interest for Each Scheme
The simple interest formula is:
\[
\text{Simple Interest} = \text{Principal} \times \text{Rate} \times \text{Time}
\]

For Scheme A:
- Principal: \( x \)
- Rate: 14% per annum
- Time: 2 years

\[
\text{Simple Interest from A} = x \times \frac{14}{100} \times 2 = 0.28x
\]

For Scheme B:
- Principal: \( 13,900 - x \)
- Rate: 11% per annum
- Time: 2 years

\[
\text{Simple Interest from B} = (13,900 - x) \times \frac{11}{100} \times 2 = 0.22 \times (13,900 - x)
\]

Total Simple Interest
\[
\text{Total Simple Interest} = 0.28x + 0.22 \times (13,900 - x) = 3,508
\]

 Solve for \( x \)
First, simplify the equation:
\[
0.28x + 0.22 \times 13,900 - 0.22x = 3,508
\]
\[
0.28x - 0.22x + 3,058 = 3,508
\]
\[
0.06x + 3,058 = 3,508
\]
\[
0.06x = 3,508 - 3,058
\]
\[
0.06x = 450
\]
\[
x = \frac{450}{0.06}
\]
\[
x = 7,500
\]

Amount invested in Scheme B
\[
\text{Amount invested in Scheme B} = 13,900 - x
\]
\[
= 13,900 - 7,500
\]
\[
= 6,400
\]

So, the amount invested in Scheme B is TK 6,400.