If Rs. 1200 amounts to RS. 1740 in 5 years ,find that will amount to Rs. 2720 in 4 years at the same rate of interestper anum.

Answer :

We know formula for simple interest = $\frac{\mathrm{P} \times \mathrm{r} \times \mathrm{t}}{100}$

So, from first condition we get

$$\begin{gathered} 1740 - 1200 = \frac{1200 \times r \times 5}{100} \\ \Rightarrow 540 = \frac{12 \times r \times 5}{1 } \\ \Rightarrow 540 = 60 r \\ \mathbf{\Rightarrow }\mathit{r}\mathbf{ }\mathbf{=}\mathbf{9} \end{gathered}$$
Then , Interest for rate 9% for 4 year on Rs 2720 = $\frac{2720 \times 9 \times 4}{100} = \frac{272 \times 9 \times 4}{10 } = \frac{9792}{10} =\mathbf{ }\mathbf{Rs}\mathbf{.}\mathbf{ }\mathbf{979}\mathbf{.}\mathbf{20}$

Therefore, amount will became =  2720 + 979.20 =  Rs. 3699.20                              (Ans )