Correct Answer - Option 3 : Rs. 100

**Given****∶**

Some money was invested at the rate of 37% S.I. .

He received Rs. 123 as interest.

And some money was invested at the rate of 43% S.I.

When the amount was interchanged, The interest He received is Rs.(123 - 6) 117.

**Formula** **Used**∶

S.I =PRT/100

Basics of Linear Equations.

**Calculation∶**

Let the amount invested at 37% = Rs. x

And amount invested at 43% = Rs. y

According to Question,

123 = (x × 37 × 1)/100 + ( y × 43 × 1)/100

⇒ 37x + 43 y = 12300 (1)

Also, 117 = (43 × x × 1)/100 + (37 × y × 1)/100

⇒ 43x + 37 y = 11700 (2)

On adding eq.(1) and eq.(2) we get,

x + y = 300 (3)

On subtracting eq.(1) and eq.(2) we get,

y - x = 100 (4)

On adding eq.(3) and eq.(4) we get,

2y = 400

⇒ y = 200 and x = 100

**∴ Amount received at 37% is Rs.100.**