Peter is making an "x marks the spot" flag for a treasure hunt. the flag is made of a square white flag with sides of 121212 inches. he will make the "x" by stretching red ribbon diagonally from corner to corner. how many inches of ribbon will peter need to make the "x"?

To mark X spot, the ribbon should be stretched diagonally from one end to another. Since the flag is a square, a diagonal cuts the square into 2 equal triangles. The diagonal length is the hypotenuse of the triangle, as the triangles formed are 2 right angled triangles.
Using Pythogoras' theorem, hypotenuse can be found out with the following equation;
H² = X² +X²
where H is the hypotenuse in other words the diagonal
X - length of the triangle, since its a square all lengths are equal
X- 12 inches
H² = 12² + 12²
    = 144+144 
H² = 288
H = 16.9 inches≈17 inches
to make the mark X he will need 2 strips of ribbons of length 17 inches each.
total length of the ribbon needed = 34 inches