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#1
Posted to microsoft.public.excel.worksheet.functions
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I just had to tell someone...
Hi,
Myself and a colleague have been trying to work out how to calculate the number of years it will take to achieve a target value (which grows at a seperate slower rate) given a pre-defined start value and fixed growth using a single formula and just did it...and really felt the need to tell someone!! Start Value B4 = 14216 Growth Rate B5 = 1.07 Target Value B6 = 17750 Growth Rate B7 = 1.02 Duration: =LOG(((B6*B7^B10)/B4),B5) Am sure there are better ways and any high school student could have done this but we're old so we feel dead chuffed!! Anyway, glad to get that out of the system :-) Best Regards, CalumMurdo Kennedy |
#2
Posted to microsoft.public.excel.worksheet.functions
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I just had to tell someone...
It is hard to check if your formula returns a correct value or not because
it uses the cell B10 which you didn't define for us. With that said, the formula I derived is different than yours (and requires only the cells you defined for us). I get this formula... =LOG(B6/B4)/LOG(B5/B7) Here is how I developed it (X is the unknown time period we are looking for)... B4 * (B5 ^ X) = B6 * (B7 ^ X) Log(B4 * (B5 ^ X)) = Log(B6 * (B7 ^ X)) Log(B4) + Log(B5 ^ X) = Log(B6) + Log(B7 ^ X) Log(B4) + (X * Log(B5)) = Log(B6) + (X * Log(B7)) (X * Log(B5)) - (X * Log(B7)) = Log(B6) - Log(B4) X * (Log(B5) - Log(B7)) = Log(B6) - Log(B4) X * Log(B5 / B7) = Log(B6 / B4) X = Log(B6 / B4) / Log(B5 / B7) -- Rick (MVP - Excel) wrote in message ... Hi, Myself and a colleague have been trying to work out how to calculate the number of years it will take to achieve a target value (which grows at a seperate slower rate) given a pre-defined start value and fixed growth using a single formula and just did it...and really felt the need to tell someone!! Start Value B4 = 14216 Growth Rate B5 = 1.07 Target Value B6 = 17750 Growth Rate B7 = 1.02 Duration: =LOG(((B6*B7^B10)/B4),B5) Am sure there are better ways and any high school student could have done this but we're old so we feel dead chuffed!! Anyway, glad to get that out of the system :-) Best Regards, CalumMurdo Kennedy |
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