40,20,?,40,20,10? ? = 10 Because, the sequence is 40,20,10 and then replay it again or 40 - 20 = 20 20 - 10 = 10 40 - 20 = 20 20 - 10 = 10 So, ? = 10

It is 10 that ìs missing because the sequence shows that after 20 is 10