Question

In circle O, AD and BE are diameters. The measure of arc AB is 55° and the

measure of arc CD is 25º.
What is the measure of BC?
80
110
90
100

Answer 1

Arc AB = 55°

Angle AOB = 55° ( Centre angle is equal to respective arc )

Arc CD = 25°

Angle COD = 25° ( Centre angle is equal to respective arc )

Angle AOB + Angle BOC + Angle COD = 180° ( AD is the diameter)

55° + Angle BOC + 25° = 180°

Angle BOC + 80° = 180°

Angle BOC = 100°

Answer 2

100. the diameter means the other half, so arc AD is 180 on both sides. so that means we can do 180-(25+55), which equals 100