Understand the rule first
List features added, removed and shared. When shapes overlap, count shared boundaries or marks according to the stated rule—once if retained, or not at all if they cancel.
Combine, remove and count visual features without double-counting overlaps.
List features added, removed and shared. When shapes overlap, count shared boundaries or marks according to the stated rule—once if retained, or not at all if they cancel.
Adding every count automatically even when features overlap or are removed.
Reusable method: List added, removed and unchanged features separately.Coincident outlines occupy the same visible boundary.
Answer B: 1
Only one square outline is visible.
Quick method: List added, removed and unchanged features separately.
Add all edges, then remove both counts of the internal shared side.
Answer C: 5
3 + 4 − 2 = 5 outer edges.
Quick method: List added, removed and unchanged features separately.
Removing every second dot removes half of them.
Answer D: 4
Half of 8 is 4, so 4 remain.
Quick method: List added, removed and unchanged features separately.
Subtract the overlap once after adding both group counts.
Answer A: 9
7 + 5 − 3 = 9 distinct items.
Quick method: List added, removed and unchanged features separately.
The left mark appears twice and cancels.
Answer B: top and bottom
Only the top and bottom marks remain.
Quick method: List added, removed and unchanged features separately.
Add both groups and subtract the overlap once.
Answer B: 11
9 + 6 − 4 = 11.
Quick method: List added, removed and unchanged features separately.
The boundaries occupy the same position.
Answer C: 1
Only one triangle outline remains visible.
Quick method: List added, removed and unchanged features separately.
Apply the removal before the addition.
Answer D: 9
10 − 3 + 2 = 9.
Quick method: List added, removed and unchanged features separately.