Interest calculation

Question

My question is if suppose I lend someone 10000 indian rupees and he is paying me back daily 100 rs for 120 days .. how much interest I am earning ?

Answer 1

100 * 120 = 12000

12000 - 10000 = 2000

He paid you back 2,000 rs in interest, which is 20% of 10000 (easily calculate by first finding 10% by moving the decimal point one place to the left and multiplying by 2, since 20% is double 10%)