Question

Given, line l and line m are parallel. If m∠1 = 60°, and m∠2 = 125°, what is m∠3?

95°
105°
115°
125°

Answer 1

Refer to the figure shown below.

Because the sum of angles on a straight line is 180°, therefore
m∠2 + m∠x = 180°
125° + m∠x = 180°
m∠x = 180 - 125 = 55°

Because the sum of angles in a triangle is 180°, therefore
m∠1 + m∠x + m∠y = 180
60 + 55 + m∠y = 180
m∠y = 180 - 60 - 55 = 65°

Because the sum of angles on a straight line is 180°, therefore
m∠3 + m∠y = 180
m∠3 + 65 = 180
m∠3 = 180 - 65 = 115°

Answer: m∠3 = 115°