In the table below, 1:2, 2:4, 3:6, 4:8, and so on are all equivalent ratios. A multiplication table. In the row labeled 1, the numbers 1, 2, 3, 4, 5, 6, 7, 8 and 9 are highlighted. In the row labeled 2, the numbers 2, 4, 6, 8, 10, 12, 14, 16, and 18 are highlighted.

By what factor is the first term in each ratio multiplied to get the second term?
1
2
3
4