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

1 Answer
Mar 27, 2018

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.