Question

If a sum of rs 800 amounts to rs 1280 in 5 years at certain rate, what some amounts to rs 2400 in 5 years at the same rate?

Answer 1

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?

Step-by-step 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,

`\begin{gathered} A=1280 \\ P+SI=1280 \\ P+(Pnr)/(100)=1280 \\ 800+(800*5* r)/(100)=1280 \\ 40r=1280-800 \\ 40r=480 \\ r=(480)/(40) \\ r=12 \end{gathered}`

Hence, the rate is 12%.

Also,

Let P be the principal amount.

Then,

`\begin{gathered} A=2400 \\ P+SI=2400 \\ P+(Pnr)/(100)=2400 \\ P+(P*5*12)/(100)=2400 \\ (100P+60P)/(100)=2400 \\ (160P)/(100)=2400 \\ (16)/(10)P=2400 \\ P=(2400*10)/(16) \\ P=1500 \end{gathered}`

Hence, the principal amount is Rs. 1500.