Final answer:
To find the perimeter of two regular pentagons placed close together, multiply the length of one side by 9 since they share a side. The perimeter is 22.5 cm.
Step-by-step explanation:
The question is asking for the perimeter of a new shape formed when two regular pentagons are placed close together. Since a regular pentagon has equal side lengths, the perimeter of one regular pentagon is the sum of its five sides. If one regular pentagon has a perimeter of 12.5 cm, then each side measures 2.5 cm (because 12.5 cm divided by 5 is 2.5 cm).
When two regular pentagons are placed close together, they share a side. Therefore, instead of calculating the sum of 10 sides (5 sides for each pentagon), we calculate the sum of 9 sides. So the new perimeter is 9 × 2.5 cm = 22.5 cm.