Perimeter counting on a square fence: Compute total poles when corners are shared. Context: Square plot with 27 fence poles on each side. Corner poles are common to two sides and must not be double-counted. Choose the correct total number of poles used.

Given data & concept

• Each side lists 27 poles, which includes both corner poles for that side.
• Naively summing gives 4 × 27 = 108 counts, but the four corner poles are double-counted.

Step-by-Step calculation
Total (naive) = 4 × 27 = 108 Adjust for 4 corners counted twice: 108 − 4 = 104

Common pitfalls
Forgetting to subtract the 4 overcounts at the corners.

Final Answer
104