Question

A sum of money double itself 8 years. What is the rate of interest

Answer 1

Let Sum of Money(Principle)=₹100

In 8 year it Become Double.

After 8 year Total amount

100×2=₹200

SI=Amount-Principle

SI=200-100

SI=₹100

We Got.

Principle(p)=₹100

Time(t)=8 years

SI=₹100

Rate(r)=r%

We know.

SI=P×R×T/100

$\frac{\cancel{100} \times 8 \times r}{\cancel{100}} = 100 \\ \\ 8r = 100 \\ \\ r = \frac{\cancel{100}}{\cancel{8}} \\ \\ r = \frac{25}{2}$

In Mixed Fraction

$Rate = 12 \frac{1}{2} \%$

Answer 2

$\underline{\underline{\huge{\textbf{Question:}}}}$

A sum of money double itself in 8 years. What is the rate of interest ?

$\underline{\huge{\textbf{Solution:}}}$

$\bold{\textsf{Let the principle be Rs. x.}}$

Given :

• It becomes double in 8 years .

So

Amount = 2 × $\bold{x=Rs.2x.}$

We know that ,

• Simple Interest = Amount - Principle

                                  = Rs.(2x - x) = Rs. x.

Now we have :

• SI = Rs. x
• Time = 8 years.
• Principle = Rs.x

To find :

• Rate = ?

$\bold{\boxed{\mathbf{Rate=\frac{SI*100}{Principle*Time}}}}\\\\\\\bold{\mathbf{=\frac{x*100}{x*8}}}\\\\\\\bold{=\frac{100}{8}=\frac{25}{2}=12\frac{1}{2}\%.}\\\\\\\bold{\boxed{\mathbf{Rate=12\frac{1}{2}\%.}}}$