Amanda has a 2-cm rod, a 5-cm rod and a 9-cm rod. She will randomly choose a fourth rod from a box containing rods of lengths 2, 4, 6, 8, 10, 12, 14, 16, 18 and 20 cm. What is the probability that Amanda’s four rods will be able to form a convex quadrilateral, if the rods are to be connected endpoint to endpoint? Express your answer as a common fraction.
