One of the two people is missing two, so if we give the old man two more pears, each old man will only get two pears. At this time, if each old man takes a pear, there are just three more pears (1 person, one more 1 plus two), and the number of extra pears is exactly the number of old people, that is, three old people.
In this way, the number of pears is easily calculated to be four.