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InTheBlack · 03-07-2020, 14:54

calculating doubling time -- My brain hurts... used to be able to do this with logarithm formula, but stumped on the phrasing; growth at "the rate of 10 folds every 19 days."

How do you turn that into a % growth rate to plug into a D.T. formula?

EDIT: it has a 10x time of 19. What is the 2x time?

EDIT: by brute force, x^y is 1.129^19 days = 10.03 fold increase
So "rate" is 12.9% per day

using that rate is a doubling time of 5.71 days
https://miniwebtool.com/doubling-time-calculator/?r=19

***
BETTER:

2 = e^rt

ln(2) = ln (e^rt)

ln(2) = rt

( ln(2) / t ) = r

except use ln(10) for 10x instead of 2x.
rate is 12.1%
DT is 6.07 days

The moral of this is that really small changes in exponent values make big changes in the final result, so its probably between 5.5 and 6.5 days...

03-07-2020, 14:54	#363
InTheBlack BANNED USER Join Date: May 2006 Posts: 249	calculating doubling time -- My brain hurts... used to be able to do this with logarithm formula, but stumped on the phrasing; growth at "the rate of 10 folds every 19 days." How do you turn that into a % growth rate to plug into a D.T. formula? EDIT: it has a 10x time of 19. What is the 2x time? EDIT: by brute force, x^y is 1.129^19 days = 10.03 fold increase So "rate" is 12.9% per day using that rate is a doubling time of 5.71 days https://miniwebtool.com/doubling-time-calculator/?r=19 *** BETTER: 2 = e^rt ln(2) = ln (e^rt) ln(2) = rt ( ln(2) / t ) = r except use ln(10) for 10x instead of 2x. rate is 12.1% DT is 6.07 days The moral of this is that really small changes in exponent values make big changes in the final result, so its probably between 5.5 and 6.5 days... Last edited by InTheBlack; 03-07-2020 at 16:10.
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