.
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.
Solved.
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To see many other similar (and different) solved problems, look into the lessons
- Compound interest percentage problems
- Problems on discretely compound accounts
in this site, and learn the subject from there.
After reading these lessons, you will tackle such problems on your own without asking for help from outside.
Also, you have this free of charge online textbook in ALGEBRA-I in this site
- ALGEBRA-I - YOUR ONLINE TEXTBOOK.
The referred lessons are the part of this online textbook under the topic "Logarithms".
Save the link to this online textbook together with its description
Free of charge online textbook in ALGEBRA-I
https://www.algebra.com/algebra/homework/quadratic/lessons/ALGEBRA-I-YOUR-ONLINE-TEXTBOOK.lesson
to your archive and use it when it is needed.
Happy learning (!)