7:350 Â is equivalent to 17 : 850
We first reduce the ratio to its simplest term
7:350 =7/ 350= 1/ 50
Using this simplest term 1/ 50 we can now find an equivalent ratio such that when it is reduced to its simplest term is equal to 1/ 50 Â
Reducing  17 : 950,  17 : 900  and 17 : 875 will not give an equivalent ratio of  1/ 50
17 : 850 can only  be reduced to 1/ 50 which means that the ratios 7:350  is equivalent to 17 : 850
See similar question here: link