Answer:
B
Step-by-step explanation:
So, lets go over what the rule of 72 is.
First off, the formula is:
The t stands for time in years.
The r stands for the intrest percentage.
So bascially, t is just 72 divided by the intrest rate.
So we know what the forumla/varaibles is, but what is it used for?
Well, lets plug in a number and see.
How about we go with an intrest rate of 8%? This is the most accurate percentage to use with the rule of 72, and the numbers get more and more inaccurate as you go higher or lower than this percentage:
t=72/8
=
t=9
So we know that it takes 9 years to do...what exactly?
Well, lets see, if you multiply 72 by 108% 9 times, what do you get? Remember that parehteses are important, and if you are testing this on a calculator, you should do 72*(1.08^9):
Well, 1.08 to the ninth power is 1.999
Times this by 72, and you get: 143.28
This is not 100% accurate, but as you can see, its very close to DOUBLING the value.
So, we know that it would take 9 years in this situation to double our value, or in other words:
9 years is the approximent time it takes to double our value, or investment.
This looks almosted exactly like B.
Hope this helps!