Answer: 256 bacterium.
Explanation:
suppose a bacterium would divide once in every half an hour, this means it would be double in half an hour.
therefore, a number of the bacterium after half an hour will be 1 x 2 = 2.
After one hour, we would have doubled the number of bacterium =2 x 2
= 4.
Also, in one and a half hours, it would become 4 x 2
= 8.
In 2 hours, it would be 8 x 2 = 16.
Also in two and half hours, it would be 16 x 2
= 32.
In three hours, it would be 32 x 2
= 64.
In three and a half hours, it would be 64 x 2
= 128.
Funally, in four hours, the number of bacterium would have been multiplied to 128 x 2
= 256.
