Given:
- Initial number of bacteria = 10
- Reproduction time = every 20 minutes
- Total time = 2 hours = 120 minutes
Since bacteria reproduce every 20 minutes:
Number of cycles $=\frac{120}{20} = 6$
Each bacterium splits into 2. So after each cycle, the number of bacteria doubles. That means after n cycles, the population multiplies by $2^n$ .
Hence final count of bacteria would be $ = 10 \times 2^6 = 640$