Explanation

The sequence 5, 10, 20, 40, 80, .... is an example of a geometric sequence.

5 + 5 = 10

10 + 10 = 20

20 + 20 = 40 

40 + 40 = 80

The pattern is that we are always multiplying by a fixed number of 2 to the previous term to get to the next term.1