Amoeba which self double every second and fills entire room in 1 hour. When will amoeba fill a half the room?

Question

If in a room there is an amoeba and he make him self double every second and will fill the entire room in 1 hour. When (in seconds) will amoeba fill a half the room?

Answer 1

When 3599 seconds will amoeba fill a half the room, The next second is 3600, that is 1 hour so that is doubled and fill the room .

Answer 2

1 second less from 1 hour = 3600 - 1 = 3599

Answer 3

1800 seconds; 30 minutes.
In the next second the room will be completely filled.