There would be 256 bacteria after one day.
There are 24 hours in a day, and the amount of bacteria doubles every 3 hours, so it will double:
24 / 3 = 8 times.
To find the current amount we could use an equation such as:
1 * 2^8 = x
Finally, solve for the number of bacteria:
1 * 2^8 = x
1 * (2 * 2 * 2 * 2 * 2 * 2 * 2 * 2) = x
1 * (4 * 4 * 4 * 4) = x
1 * (16 * 16) = x
1 * 256 = x
x = 256