As all mathematics teachers know, “before/after” problems are classic problems that our students will see most of the time.
Here are some of the tips that I have tried to teach my students.
(1) How is the “before bar” and “after bar” related? That is the most difficult part. Once the students can see the relationship, half the battle is done.
(2) Is there any implied information given in the problem ? For example, I try to get my students to see if this is a special case of before/after. Like “You give me, I give you” (where the total is constant) and “Both increased or decreased by the same amount (implied difference is constant)
(3) Is the “before bar” and “after bar” the same ? Any information given in the question that implied this
This is a very broad principles that I have when I am teaching the students the “before/after”. Of course, when I am teaching that in class, I need to unpack the questions to even more minute questions so that the students can handle. This is a skill that I am still refining. Feel free to comment if you have more tips.