National Debt??

[butterfly3]

I am seeking a way to set up this question..
If Interest on the National Debt is "X" %, how long would it take for the debt to double? How long would it take if the interest went up to "Y" percent? I am not including numbers for the simple fact I do not wantan answer. I am asking for help with setting it up. Any knowledge on my question is greatly appreciated..Thanks.

 

[mmm4444bot]

If we're talking about the United States' national debt, then I have to defer to others. That debt grows so often throughout the year that I have no idea how the interest is determined.

(Hmmm. Maybe I will ask the GGG on the WWW, later.)

 

[Denis]

d = debt
x = annual rate, like 5% = .05)
n = number of years

d(1 + x)^n = 2d

n = log(2d) / log(d(1 + x))

> If Interest on the National Debt is "X" %, how long would it take for the debt to double?
There's no need to get this exotic; this would be same thing:
If Interest on $1 "X" %, how long would it take for the dollar to double?

 

[Deleted member 4993]

There is of course rule of 72.

If the rate * time = 72, the total amount will double.

At 4% interest, it will take ~18 years to double your investment.

At 6% interest, it will take ~12 years to double your investment.

At 8% interest, it will take ~9 years to double your investment.

 

[butterfly3]

Thank all of you for helping me with this issue. It was the rule of 72, so Subhotosh Khan, you were correct and I thank you. It just so happen to be 6% for the first "X" and went up to 8% for the second "X". I believe I got it correct. 12*6=72 and 9*8=72. that is how I came up with the years, by doing the rule of 72.

 

[Deleted member 4993]

Thank all of you for helping me with this issue. It was the rule of 72, so Subhotosh Khan, you were correct and I thank you. It just so happen to be 6% for the first "X" and went up to 8% for the second "X". I believe I got it correct. 12*6=72 and 9*8=72. that is how I came up with the years, by doing the rule of 72.

Remember, rule of 72 is an approximation.

For accurate result, use the equation Denis provided you.