Question

A bacillus divides every 20 minutes under ideal conditions of food and temperature. After 3 hours what will be the number of bacilli?

a) 64 b) 128 c) 256 d) 512

Answer 1

I get `d).`

Explanation:

Well, let's say that the bacillus divides itself into `2` parts every `20` minutes.

And so, after `n` trials, there will be `2^n` bacilli. Remember that each trial `n` takes `20` minutes. So, in `3` hours, we would get:

`3color(red)cancelcolor(black)"hours"*(60 color(red)cancelcolor(black)"min")/(color(red)cancelcolor(black)"hours")*(1 \ "trial")/(20color(red)cancelcolor(black)"min")`

`=9 \ "trials"`

Therefore, there will be `2^9=512` bacilli.