Question

If a single bacteria divides in half every 20 min. how many would you have after 42 hours?

Answer 1

42 hours x (60 min/hr) = ?? minutes.
(??minutes/20 min)-1 = number of half lives.
2^half-lives = number of bacteria. A large number. Check my thinking.

Answer 2

20min = 1/3 hour
42 hours therefore = 14 doublings
2^14 = 16,384

Answer 3

If the doubling is every 20 minutes, the way I see it is that gives 3 doublings every hour or 126 doublings in 42 hours. I think my earlier post should have omitted the -1 and 2<sup>(minutes/20)= number of bacteria.

Answer 4

I think Professor Damon made a math error:
42 hours= 126 doublings
2^126= 8.5*10^37

If you are using the exponential model...

Number=originalnumber*e^(.692time/timedoubled
Number= 1*e^(..693*42/(1/3))
number= e^(.693*126)=8.4E37 The difference with the 2^126 number is due to the approximation that ln 2=.693

Answer 5

Whoops, sorry, 42*3 not 42/3

Answer 6

Right. 2^(42*60/20) = 2¹²⁶ = 8.5E37