In convex pentagon ABCDE, angles A, B and C are congruent and angles D and E are congruent. If the measure of angle A is 50 degrees less than the measure of angle D, what is the measure of angle D?
The sum of the interior angles = 540°
Let A, B , C = D - 50
And let E = D
So we have
A + B + C + D + E =540
(D -50) + (D -50) + (D -50) + D + D = 540
5D - 150 = 540
5D = 690
D = 690 / 5 = 138°
