At what percent per annum, Simple interest will double a sum of money in 12 years

Answer 1

p + pr(12) = 2p
p(1 + 12r) = 2p
1 + 12r = 2
12r = 1
r = 1/12 = appr .08333.. or 8 1/3%

consider $100
in 12 yrs, at a rate of .083333..., we would have
100 + 100(.08333..)(12) = 200
check!