# Time at which price doubles in inflation.

1. May 3, 2012

### PhysicoRaj

anybody knows how to calculate the period which a commodity which faces inflation takes to double it's price, without knowing anything except the rate of inflation? You must give a very shortcut method.
Thanks.

2. May 3, 2012

### Bignose

If X is the rate of inflation - 100/x

3. May 3, 2012

Thanks.

4. May 3, 2012

### phyzguy

Actually, a much better approximation is the "rule of 72", which is that the number of years to double at an annual growth rate of x% is 72/x. This is because (1+p)^n ~ e^(np), and ln(2) = .69. A slight correction makes it 72 instead of 69. Try it. You'll find that (1+p)^(72/p) ~=2.0 for a wide range of p.

5. May 3, 2012

### PhysicoRaj

At last!!!!!!
I was waiting for someone who told me this rule! I wanted to know if this was familiar to all. Cheeeerup!!

6. May 3, 2012

### Bignose

Is inflation compounded though? my dollar stays a dollar year to year if I hold on to it. If I take 2% off and its... I guess it makes sense to compound an inflation rate. Stupid trick question.

7. May 3, 2012

### phinds

Indirection is sleazy. If you want to know something on this forum, just ask.