What is the perimeter of a 3-4-5 triangle?

• A. 9
• B. 12
• C. 10
• D. 11

Answer: (B)

Perimeter is the total length around a shape, found by adding the lengths of all its sides. For a triangle, that means adding its three side lengths. A 3-4-5 triangle has side lengths 3, 4, and 5. Add them: 3 + 4 + 5 = 12. So the perimeter is 12. This triangle is a classic right triangle because 3^2 + 4^2 = 5^2, but that fact mainly confirms its shape; for the perimeter you just sum the side lengths.