Question

A person deposited certain money in bank at rate or 12.5% simple interest. After 2 years he again deposit Rs. 25000 and now bank gives 6% simple interest per annum at total money. At the end of 4th year his total money become 15 times itself. The find his initial investment.

Answer 1

Given :

The rate at which certain amount deposited in account = $r_1$ =  12.5% simple interest

The time period = $t_1$ = 2 years

And

After two years money deposited in account = $P_2$ = Rs 25000

The rate for amount Rs 25000 deposited in account = $r_2$ =  6 % simple interest

The time period = $t_2$ = 2 years

Total money amount = 15 time itself

To Find :

Initial investment amount

Solution :

Let the initial investment amount = $P_1$  = p

From Simple Interest method

Simple Interest = $\dfrac{Principal\times Rate\times Time}{100}$

So,

$S.I_1$ =  $\dfrac{P_1\times r_1\times t_1}{100}$

      = $\dfrac{p\times 12.5\times 2}{100}$

      = 0.25 p

∵ Amount = Principal + interest

                = p + 0.25 p

                = Rs 1.25 p

Again

$S.I_2$ =  $\dfrac{P_2\times r_2\times t_2}{100}$

      = $\dfrac{25000\times 6\times 2}{100}$

      = Rs 3000

∵ Amount = Principal + interest

                = Rs 25000 + Rs 3000

                = Rs 28000

Now, According to question

∵ The money amount at the end of 4 years = 15 time itself

i.e    Rs 1.25 p  = Rs 28000

∴                   p = $\dfrac{28000}{1.25}$

Or,         initial investment = p = Rs 22400

Hence, The initial investment amount of person in bank is Rs 22400  Answer