Question

The number of bacteria in a culture doubles every 5 minutes. At first there are 10, after 5 minutes there are 20, after 10 minutes there are 40. How many bacteria are there after 20 minutes?

a.
80
c.
60
b.
160
d.
320

Answer 1

The answer is 160 because as you stated in the question the number of bacteria doubles every five minutes, and after 10 minutes there are 40. Therefore, after 15 minutes there are 80 (40 doubled is 80), and after 20 (another 5 minutes), the number of bacteria is the double of 80, which is 160.
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