Institution: AGRANI BANK LTD Exam: Agrani bank Ltd - Officer 04.07.2008
Topic: Arithmetic Mathematics (পাটিগণিত), Subject: Mathematics (সাধারণ গণিত)

Best Answer Explained in Below-:

To determine how many years a person needs to invest Tk. 3,000 at a simple interest rate of 7% to earn Tk. 420, we can use the formula for simple interest:

\[
\text{Simple Interest (SI)} = P \times r \times t
\]

where \(P\) is the principal amount (initial investment), \(r\) is the rate of interest per year (as a decimal), and \(t\) is the time in years.

First, we convert the interest rate from a percentage to a decimal:

\[
r = \frac{7}{100} = 0.07
\]

Next, we substitute the known values into the formula. We want the simple interest to be Tk. 420, with a principal of Tk. 3,000:

\[
420 = 3000 \times 0.07 \times t
\]

Now, we can solve for \(t\):

1. First, simplify the equation:

\[
420 = 210t
\]

where \(210 = 3000 \times 0.07\).

2. Next, divide both sides by 210 to isolate \(t\):

\[
t = \frac{420}{210} = 2
\]

Thus, the person needs to invest for **2 years** to earn Tk. 420 in simple interest at a rate of 7%. Therefore, the correct option is B) 2 years.