if the simple interest on $ 2000 increase by $ 40 , when the time increase by 4 years . find the rate percent per annum .
"applying the above formula , we have 40 = 2000 * r * 4 / 100 r = 40 * 100 / 2000 * 4 = 0.5 % . answer is b"
multiply(divide(divide(40, 4), 2000), const_100)