The cost when someone borrows money from someone else is known as interest.
Interest rate is the cost of borrowing. It is the amount the borrower pays the lender for use of their funds. It is usually a function of the amount borrowed, length of the loan and the interest rate.
For example, if a person borrows $1000 for 1 year at an interest rate of 10, the interest that would be paid is: $1000 x 0.1 = $100.
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