1. The warehouse was empty, so the two cockroaches could enjoy their exercise without being disturbed. "Let's take our usual route round the edges, but in opposite directions," Rip suggested. Rap agreed, so off they went. Rap took four minutes for each circuit, Rip took 20 seconds less. They passed and re-passed each other several times. But when at last they met right at their starting point, Rip stopped. "No more for me," he declared. "You're a real old slowcoach." How many circuits had he completed?