Answer:
The population size of bacteria reaches to 6,40,000 in two hours.
Step-by-step explanation:
At the beginning, the population size of bacteria is 10000. After each 20 minutes, the population of bacteria is double. So after 20 minutes, the population of bacteria is 20000 due to splitting in two equal parts. After 40 minutes, the population reaches to 40000. By completing one hour, the population size will be 80000. After 80 minutes, the population reaches to 160000. By completing 100 minutes, the population size will be 320000. For two hours, this 320000 will be double and the population reaches to 640000.