Here is the problem set.

We give a few correct and wrong solutions to each problem below.

Go through the correct solutions. There are more than one ways to solve a problem. Is one solution better than the other?
Go through the problematic solutions also. What was the mistake?

Problem 1

Good:

answer 1

Problem 2

Good:

answer 1

Problematic:

answer 2 answer 3

Problem 3

Good:

answer 1

Problematic:

answer 2 answer 3

Problem 4

Problematic:

answer 1