Question

Which represents the series in the expanded form:

Answer 1

1 + 2 + 3 + 4 + 5
2 + 4 + 6 + 8 + 10
2 + 3 + 4 + 5
2 + 3 + 4 + 5 + 6

Answer 2

2+4+6+8+10

Answer 3

This is because you are doing the following:
2(1) + 2(2) + 2(3) + 2(4) + 2(5)