if money is invested at r percent interest , compounded annually , the amount of the investment will double in approximately 54 / r years . if joe ' s parents invested $ 5,000 in a long - term bond that pays 6 percent interest , compounded annually , what will be the approximate total amount of the investment 18 years later , when joe is ready for college ?
"since investment doubles in 54 / r years , then for r = 6 it ' ll double in 54 / 6 = ~ 9 years ( we are not asked about the exact amount so such an approximation will do ) . thus after 18 years investment will become $ 5,000 * 2 = $ 10,000 . answer : d ."
divide(multiply(multiply(add(const_2, const_3), const_1000), 6), const_2)