Answer:
10 rounds
explanation: We start with one cell. A round of mitosis doubles the number of cells.
After n rounds of mitosis, we have 2^(n) cells. After 10 rounds, we have 2^10 = 1024 cells.
If you don't see this, just start with 1 and multiply it by 2 until you get 1024. You have to do this 10 times.