If Cody cycles 10 kilometers per 2 trips, then each trip is 5 kilometers (10 km/2 trips = 5 km / 1 trip). Thus, if he wants to cycle 20 kilometers, he will have to make 20 km / X trips = 5 km. When rearranging the variables, we can say 20 km = 5 km/X trips and then 20 km / 5 km = 4 trips. Thus, Cody will do 4 trips if he cycles 20 km.