Step-by-step explanation:
m = the amount of money that is originally deposited.
x = the number of years the money is put out at 20% compound interest.
a×1.2 = a + 20% of a = a×1 + a×0.2
so, we have
m×(1.2)^x = 2m (money doubled)
(1.2)^x = 2
log1.2((1.2)^x) = log1.2(2)
x = log(2)/log(1.2) = 3.801784017... years.
remember :
loga(x) = logb(x)/logb(a)
anyway, since we are talking full years, we have to round up to the next full year : 4.
so, the least number of complete years in which a sum of money (which is put out at 20% compound interest) will be more than doubled is 4.
