A triangle has sides of 7 centimetres, 9 centimetres and 12 centimetres. Enter the number of centimetres in its perimeter.
Correct answer
28 · Accepted units: centimetres · cm
Explanation
Adding the three side lengths gives 7 plus 9 plus 12, the total amount of edge the triangle has. Stopping after two sides returns 16 and leaves a whole edge out, so the walk round the triangle would never be finished.