The ratio of an angle to its supplement is 3: 5. find the angle and it's supplement.

Givens

Call one of the angles = x

The other one is 180 - x

They are in the ratio of 3 to 5

Equation

3/5 = x / (180 - x)

Solve

3/5 = x / (180 - x)         Cross Multiply

3*(180 - x) = 5x

540 - 3x = 5x               Add 3x to both sixes

540 = 5x + 3x

540 = 8x

Divide both sides by 8

540 / 8 = x

x = 67.5

One angle is 67.5

The supplement is 180 - 67.5 = 112.5

Check

67.5/112.5 = 0.6 which is the same thing as 3/5