What is the Before-After heuristic?
Some word problems describe a change — buttons transferred, money spent, stickers given away. They tell you the situation after the change, but ask you about before.
The Before-After heuristic teaches you to draw a bar model in two states — before and after — so the relationship becomes visible and easy to solve.
Spot the keywords. When you see any of these words in a question, the Before-After heuristic is likely the right tool:
transferred
gave
moved
spent
received
at first
in the end
left over
Today's question · P3 · Chapter 3
Box A had 500 more buttons than Box B. After 120 buttons were transferred from Box A to Box B, there were 1060 buttons in Box B. How many buttons were there in Box A at first?
Read the question — identify what you know
Before picking up your pencil, read carefully and sort the information into three buckets:
Before
Box A has 500 more than Box B
Change
120 buttons move from Box A to Box B
After
Box B has 1060 buttons ← start here