The standard translation of the words to Math is THIS equation
2P = , (1)
where P is the principal amount, t is the time in years.
Canceling P in both sides, you get this equation
2 = (2)
with one unknown "t".
The standard method to solve it is to take logarithm of both sides.
It gives
log(2) = 4t*log(1+0.09/4),
t = = 7.78.
Now you need to round this number to the nearest greater integer in order for the bank
was in position to make the last compounding.
ANSWER. 8 years is required.
