Puzzles

No. 9 While exploring the jungle, three scientists were captured by a tribe of cannibals. They were given a chance to save their lives: they were tied up in such a way that scientist A could see both of the others, B could only see C, and C could see no one. They were shown five colored feathers, including three black ones and two white ones. The scientists' eyes were blindfolded, and one of the feathers was placed in each of their hair. After their eyes were uncovered, the scientists were asked to determine the color of the feather on their own head. If at least one of them answered correctly, all three would be freed. Time passes... Neither A nor B can name their color... Suddenly, scientist C, who can't actually see anyone, correctly names the color of his own feather. What thoughts led to his answer? No. 10 I am extremely young and extremely old; I am as thin as a hair and as thick as a barrel; I am the embodiment of virtue and a desperate rogue; I am blacker than ink and whiter than snow; I am as slow as a turtle and as agile as a deer; Weak as a straw and as mighty as an oak; Poor as Job and as rich as Croesus; I am a circle and a square; A ragamuffin and an aristocrat; A hurricane and a breeze; An angel and a demon; I am eternal and dead; I am constantly sick and always healthy; Lighter than a feather and heavier than lead; I am everywhere and nowhere; I am married and single. Guess: who am I?

Added 1 minute ago
They guessed he was sharpening a saw.