If the ratio of red objects to blue objects is 3: 1 then what percent of the objects are red?

In plain and short, we simply divide the "whole" by the sum of the ratios, and distribute accordingly.

now, 100% is the whole of any amount, so we'll divide 100% by (3+1).

40 & 50 in the right corner are the complementary angles as when placed in a sum (added together) they make 90°