Amanda has a 2 cm rod, a 5 cm rod, and a 9 cm rod. She will randomly chooes a fourth rod from a box containing rod of lengths 2, 4, 6, 8, 10, 12, 14, 16, 8, and 20 cm. What is the probability that Amanda four rods will be able to form a convex quadrilateral, if the rods are to be connected endpoint to endpoint?
Do you know what a convex quadrilateral is? Perhaps you would like to share this knowledge with other forum users.?
Have you tried playing with a rough sketch. If so you will be able to discound some of the possibilies straight away.
Which ones can you discount straight away, and why?