4. The problem is best solved by looking at those people who have not lost each body part. There are 30% who have not lost an eye (set A), 25% who have not lost an ear (set B), 20% who have not lost an arm (set C), and 15% who have not lost a leg (set D). The number of people who have lost all four body parts is smallest if the union of the sets A, B, C and D is as large as possible, that is, if the sets A, B, C and D are all disjoint (no overlap). If the sets A, B, C and D were all disjoint then their union would comprise 30 + 25 + 20 + 15 = 90% of the pensioners.
Hence there must be at least 100 - 90 = 10% who have lost all four body parts.