Respuesta :
Given
If a sum of Rs 800 amounts to Rs 1280 in 5 years at certain rate.
To find: What sum amounts to Rs 2400 in 5 years at the same rate?
Explanation:
It is given that,
A sum of Rs 800 amounts to Rs 1280 in 5 years at certain rate.
Let r be the rate.
Then,
[tex]\begin{gathered} A=1280 \\ P+SI=1280 \\ P+\frac{Pnr}{100}=1280 \\ 800+\frac{800\times5\times r}{100}=1280 \\ 40r=1280-800 \\ 40r=480 \\ r=\frac{480}{40} \\ r=12 \end{gathered}[/tex]Hence, the rate is 12%.
Also,
Let P be the principal amount.
Then,
[tex]\begin{gathered} A=2400 \\ P+SI=2400 \\ P+\frac{Pnr}{100}=2400 \\ P+\frac{P\times5\times12}{100}=2400 \\ \frac{100P+60P}{100}=2400 \\ \frac{160P}{100}=2400 \\ \frac{16}{10}P=2400 \\ P=\frac{2400\times10}{16} \\ P=1500 \end{gathered}[/tex]Hence, the principal amount is Rs. 1500.
