A certain money amounts `9440Rs` on simple interest in `3` years. If the rate of simple interest be `25%` increased per annum, then the money will become `9800Rs` after same period of time. Find the principal and the rate of interest in percent per annum.

Explanation

The difference between two given amounts `=Rs(9800-9440)=360Rs`
Since the principal and period of time are the same, we can say that due to `25%` increase of interest, the increase in amount is `Rs360`
`:.25%` of interest `=Rs360`
`1%` of interest `Rs(360)/(25)`
`100%` of interest `=Rs(360)/(25)`
`100%` of interest `=Rs(360xx100)/(25)=Rs1440`
`:.` Simple interest in `3` years `=Rs1440`
So, the principal `=Rs(9440-1440)=Rs8000`
Now, let the rate of interest be `r%` in percent per annum
`:.(8000xxrxx3)/(100)=1440impliesr=(1440xx100)/(8000xx3)=6`
`:.` The required principal `=8000Rs` and rate of interest in percent per annum `=6%`.