In following number series, two terms have been put within brackets. Choose the appropriate option - Look at this series: 1000, 200, 40, . . . What number should come next?

Answer: A. 8

This is a simple division series.
Each number is divided by 5.
Rule = (1st number / 5 = 2nd number) (2nd number / 5 = 3rd number)....
Now, (1000 / 5 = 200), (200 / 5 = 40), (40 / 5 = 8)...
So answer is a = 8.