Sequence 40 20 10 40 20?

10. if you break it down it becomes 10.

40 to 20 is 20

20 to 10 is 10

10 to 40 is 30

40 to 20 is 20

now if you take the difference between those and break those down its

20 to 10 is 10

10 to 30 is 20

30 to 20 is 10

now if you break those down its

10 to 20 is 10

20 to 10 is 10

10 is your final answer