Question 1109899
What form of growth is expected?


{{{y=a*b^x}}}


{{{system(400=a*b^3,660=a*b^5)}}}


{{{660/400=(ab^5)/(ab^3)}}}


{{{b^2=1.65}}}


{{{b=1.2845}}}

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{{{a=400/b^3}}}

{{{a=400/(1.2845^3)}}}

{{{a=188.7}}}

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From 5 years to 8 years is a change by 3 years.
Start value from 5 years was 660.
{{{660*1.2845^3}}}

{{{1399}}}

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Alternate:
{{{188*1.2845^8}}}


{{{1393}}}, nearly the same as {{{1399}}}...

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If you want a linear fit model, then the procedure is different and gives a different value.