13.

Two complementary angles are in the ratio of 4:5. Find the measure of the smaller angle.

The smaller angle = 40 degrees.

Step-by-step explanation:

If one angle is x the other is 90-x (because they are complementary).

If we split 90 degrees into 4+5 = 9 parts one part = 10 degrees and the 2 angles in the ratio 4:5 must be 4*10 and 50 * 10.