how long does it take an investment to quadruple in value if it earns 4% simple interest per year?
4 = 4% x y
4 =0.04 x y divide both sides by 0.04
y =4 / 0.04 = 100 years for $1 to grow to $4 at simple interest of 4%.
P.S. compare this to 4% compounded annually at which you will quadruple your money in about 35 years.
+16 
