`10Rs` is given as a loan to someone in such a condition that he will pay back the loan in `11` instalments at the rate of `1Rs` per instalment. Find the rate of simple interest per annum.

Explanation

Let the rate of annual simple interest be `r%`
Here, `Rs10+` simple interest of `Rs 10` for `11` months.
`=Rs 10+` simple interest of `Rs 1` for `(1+2+3+……..+10)` months
`=Rs10+` simple interest of `Rs 1` for `55` months
`=` Simple interest of `Rs1` for `55` months
`=Rs1`.
`:. (1xx55xxr)/(100xx12)=1impliesr=(240)/(11)=21(9)/(11)`
`:.` The rate of simple interest `=21(9)/(11)%` per annum.