Answer:
400
Step-by-step explanation:
The current number is 100, it doubles every ten days, and you're asking what the size will be in twenty days.
Beginning:
100 ants (ten days pass)
100 x 2 = 200
Middle:
10 of the 20 days have passed
Your new number is 200 ants
End:
200 ants (ten days pass)
Since every ten days the size doubles: 200 x 2 = 400
400 ants after 20 days
