An octopus has 8 arms. A starfish has 5 arms.
How many fewer arms does the starfish have than the octopus?

answer: the prove is mentioned below.

step-by-step explanation:

an isometric rigid transformation is a transformation of the plane that preserves lengths and angles.    

that is, the pre-image and the image under a rigid transformation will be congruent.

here, given: cb ║ ed and cb ≅ ed

prove that: δ cbf ≅ δ edf

since, cb ║ ed

therefore, by the alternative interior angle theorem,

∠fcb ≅ ∠fed

∠fbc ≅ ∠ fde

and, cb ≅ ed ( given)

therefore, the angles and sides are persevered after transformation.

thus, by the definition of isometric rigid transformation,

δ cbf ≅ δ edf

your answer would be 1/6