Question

55:100 66:120 are these ratios equivalent ?

Answer 1

Yes they are because if you simplify them both then they both equal 11:20 
so they are equivalent ratios

Answer 2

The way to solve this is to simplify the ratios. 55 and 100 can both be divided by 5 to get 11:20. 66 and 120 can both be divided by 6 to get 11:20. Since the traps simplify to the same thing, yes, they are equivalent.