36. A student invested 3000 dollars of his student loan. Then received an interest of 400 dollars over 4 years. Question: Find the interest rate per year. => 400 dollars is for 4 years of interest. => 400 / 4 = 100 dollars is the per year interest, now, let’s solve its percentage of interest rate. => 100 dollars / 3 000 dollars = 0.03 => 0.03 * 100% = 3% Thus, a student earned 3% annual interest rate for her 3000 dollars.