If l || m, m∠A + m∠B = 120°, and m∠D = 65°, what is m∠A?

Look at the picture. Line ’ l ’ is parallel to line ’ m ’, and the horizontal line on the bottom (which is not labeled) is a transversal that cuts the parallel lines.

Did you learn that interior angles on the same side of the transversal are equal?

I’m sure you did, although it may have a new name nowadays.

Anyway, with the help of that ’tool’, angle-’B’ and angle-’D’ are equal. So.

(angle-A + angle-B) = 120

angle-B = 65

angle-A = 120 - 65 = **55 degrees**.

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