In an experiment to compare two different types of long-lasting razor blades, A and B, 20 men were asked to shave with a blade of type A for one week and then with a blade of type B for one week. At the end of this period, 15 men thought that blade A gave a smoother shave than blade B. and the other 5 men thought that blade B gave a smoother shave. Test the null hypothesis that blade A does not tend to give a smoother shave than blade B against the alternative that blade A tends to give a smoother shave than blade B.