How many years will it take to double an investment at 11% simple interest

With SIMPLE interest you add the same amount if interest each year. In total you add i= Prt for t years.

So if you want your money to double, you must accumulate $P in interest, so, i = P(0.11)t must = P

Cancel the Ps and solve 0.11 t = 1.

So t = 1/0.11 = 9.09 ... approx. A little over 9 years.

0.11 n =1 , solve for n , number of years