A sum, when invested at 10% simple interest per annum, amounts to ₹4080 after 2years. What is the simple interest (in ₹) on the same sum at the same rate of interest in1 year?

Correct option is D

Given:

Rate of interest R = 10% per annum

Time T = 2 years

Amount A = ₹4080

Formula Used:

A = P + SI

SI = $$\frac{P \times R \times T}{100}$$​​

Solution:

Let principal be P

SI = A - P

Also,

SI = $$\frac{P \times 10 \times 2}{100}$$​

​$$= \frac{20P}{100} = 0.2P$$​​

So,

A = P + SI = P + 0.2P = 1.2P

Given A = 4080,

​$$1.2P = 4080 \implies P = \frac{4080}{1.2} = 3400$$​​

Now, simple interest for 1 year:

SI = $$\frac{3400 \times 10 \times 1}{100} = 340$$​​

Simple interest in 1 year = ₹340

Alternate Solution: ​

​$$10\% = \frac{1\rightarrow SI}{10\rightarrow Principle}$$ 

For two year SI will be 2 

Total amount will be 10 + 2 = 12 

12 unit = 4080 

1 unit = 340 

Thus , 1 year SI = ₹340