This is exponential growth...
f=ir^t, f=final amount, i=initial amount, r=rate, t=time
f=2r^t so we have a point at ten minutes that says:
8=2r^10
4=r^10
r=4^(1/10) so our equation is:
f=2(4^(1/10)^t)
f=2(4^(t/10)) now we wish to solve for t when f=16
16=2(4^(t/10))
8=4^(t/10) taking the natural log of both sides...
ln8=(t/10)ln4
t/10=ln8/ln4
t=10(ln8/ln4)
t=15
So after fifteen minutes there will be 16 cells in the bottle...
10:05+:15=10:20
So at 10:20 there will be 16 cells in the bottle.