The amount of bacteria doubles every day. If there are 320 bacteria on day 6, when will there be 5,120 bacteria?

Day 10

Explanation:

If the number of bacteria increases by a factor of two each day (i. e. it doubles), it will reach 5120 by day 10. At this rate, the colony likely started with 10 bacteria on day one and doubled each day to reach 320 by day 6.

Day 6 - 320 bacteria

Day 7 - 320*2 = 640 bacteria

Day 8 - 640*2 = 1280 bacteria

Day 9 - 1280*2 = 2560 bacteria

Day 10 - 2560*2 = 5120 bacteria