Question

After 6 yrs. , a sum
invested at simple
interest at the rate of R% becomes
twice
of itself what
value of 'R'?​

Answer 1

Answer:

Let x % be the simple interest per annum on Principal amount(P) you deposited.

After 1 year your money will become P + x% P.

After 2 year your money will become P + x%P + x% P.

Similarly, After 6 years your money will become P + 6 (x% P).

Now According to Question, this amount after 6 years is 2 times the amount you deposited i.e P.

Mathematically it can be expressed as,

2P = P + 6 (x% P) ……………(i)

From here, x = 100/6.

Now let’s assume that after n years, your amount gets 4 times the amount you deposited i.e P.

Mathematically it can be expressed as,

4P = P + n (1/6 P) { Since x = 100/6, Therefore x% = 1/6} ………… (ii)

From equation (ii),

n = 18 years.

Therefore, this means that if you want to Quadruple your deposited amount with a simple interest of 1/6 % per annum. You have to wait for 18 years.

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