In which step did the student first make a mistake and how can it be corrected?

Step 1: It should be m∠m + m∠n + m∠o = 180° (sum of angles in a triangle)

Step-by-step explanation:

He made the mistake in Step 1: m∠m + m∠n + m∠p = 180°

It should be m∠m + m∠n + m∠o = 180°

Then only, he can equate it with m∠o + m∠p in step 3.

So,  m∠p is the exterior angle and m∠m and m∠n are the two remote interior angles.

m∠o is the adjacent angle to m∠p. They form a linear pair.

Hence, the correct answer is Step 1.

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