Explanation:
you multiply both sides by the same factor, so that the main message or information, the ratio, stays the same :
3:6 × 2/2 = 6:12
3:6 × 1/3 / 1/3 = 1:2
3:6 × 4/3 / 4/3 = 4:8
3:6 × 100/100 = 300:600
so, these are all equivalent ratios. and there are infinitely more, as you can see.