Total amount to be paid back = 11₹, which should be equal to Principal + Simple Interest.

Here Principal = 10₹, so simple interest = 1₹.

Simple Interest = (principal x rate of interest x time period)/100.

So rate of interest = (S.I. x 100)/(principal x timeperiod).

Rate of interest = (1 x 100)/(10 x 11) = 10/11= 0.91% per month.