Find the angles of a parallelogram if three of them add up to 300 degrees.

Given:
АВСК – parallelogram,
angle A + angle B + angle C = 300 degrees.
Find the degree measures of angle A, angle B, angle C, angle K -?
Decision:
Consider the parallelogram ABСK.
Its opposite angles are equal to each other, then angle A = angle C, angle B = angle K.
The sum of the degree measures of all angles of the parallelogram is 360 degrees.
Hence:
angle A + angle B + angle C + angle K = 360;
300 + angle K = 360;
angle K = 360 – 300;
angle K = 60 degrees;
Angle K = angle B = 60 degrees;
angle A = angle C = (360 – 120): 2;
angle A = angle C = 120 degrees.
Answer: 60 degrees; 60 degrees; 120 degrees; 120 degrees.