Question 1169252
A=Aob^x
400=Ao^b^10
1200=Ao^b^30
3=b^20
b=3^(1/20)=1.056
not rounding
1200=Aob^30=Ao*3^1.5
Ao=230.94 or 231 organisms
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A=231*3^0.05^x
Doubling is when
2=3^0.05^x
or ln 2=x ln 3^0.05
ln2=0.05x ln 3
20 ln2=x ln3
x=12.619 min or 12.6 min.
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tripling time is 3=1.056^x or 
20 ln 3=x ln 3
x=20 minutes, which it should be.
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after 80 minutes
A=231(3^0.05)^80=231^3^4
=18,711 organisms
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14000=231*3^0.05x
60.606=3^(0.05)^x 
ln 60.606=x*0.05 ln 3
82.088=x ln3
x=74.72 min

{{{graph(300,300,-100,100,-1000,20000,231*3^(0.05x))}}}

{{{graph(300,300,-10,40,-100,2000,231*3^(0.05x))}}}