Answer:
12.08 years
Explanation:
to overcome this problem we will have to use the exponential growth formula A = P(1+r)^t
where a is the final amount
where p is the initial amount
where r is the rate per year
where t is the number of years
we can say
20= 2(1+0.21)^t
solve the equation for t
20/2 = 2(1.21)^t/2
10 = 1.21^t
take the log of both sides we get that
t = 12.08 years