Draw the bar model
We draw three stages: Before, Transfer, and After. The key is keeping Box A and Box B's blue bars the same width throughout — they represent the same base quantity.
Before
Box A
Box B
Box A is 500 more than Box B
Why the same width? Box A and Box B start with the same base amount — only the extra 500 makes Box A longer. Drawing them aligned makes this crystal clear.
Transfer — 120 buttons move from A to B
Box A
loses 120
Box B
gains 120
The 120 that leaves Box A is the same 120 that enters Box B
After
Box B
Key insight: 1060 is Box B after receiving 120. The bracket arrow shows the total we know. From here we work backwards to find what we don't know.
What to notice
Box A in the Transfer row is exactly the same total width as Box A in the Before row — the 500 is just split into 380 remaining and 120 leaving. This is the power of the bar model: the relationship stays visible across all three stages.