Select the number from the given options that can replace the question mark (?) in the following series.
40, 50, 30, 60, 20, ?

Given: 40, 50, 30, 60, 20, ?

Logic: In this given number series the +10, -20, +30, -40, +50 pattern follows

40+10=50

50-20=30

30+30=60

60-40=20

20+50=70

So, missing number = 70