How are the ratios 100/2, 150/3, 175/3.5, 200/4 related to 50/1?

The ratios are all proportional to 50/1.

Ratios are proportional when its cross products are equal.
a/b = c/d where ad = cb

100/2 is proportional to 50/1 because 100*1 = 2*50 ⇒ 100 = 100
150/3 is proportional to 50/1 because 150*1 = 3*50 ⇒ 150 = 150
175/3.5 is proportional to 50/1 because 175*1 = 3.5*50 ⇒175 = 175
200/4 is proportional to 50/1 because 200*1 = 4*50 ⇒ 200 = 200