Suppose a family has two children and you know at least one is a boy. Intuition says the chance both are boys is one half, but it is one third. Among two-child families there are four equally likely combinations: boy-boy, boy-girl, girl-boy and girl-girl. Learning that at least one is a boy rules out only girl-girl, leaving three cases, and just one of them is boy-boy. The answer changes with how the information was obtained: if you learned that a specific child, such as the older one, is a boy, the chance the other is also a boy becomes one half. Martin Gardner popularised the puzzle in Scientific American in 1959, and it became a classic demonstration that wording and procedure shape probability.

Hampi is a UNESCO World Heritage Site in Karnataka, India, with more than 1,600 surviving remains spread over 4,100 hectares. It was the capital of the Vijayanagara Empire from 1336 to 1565. Travellers from Persia and Portugal described it as a prosperous, wealthy and grand city with temples, markets and farms along the Tungabhadra River. By 1500 it was estimated to be the world's second-largest city after Beijing, and probably India's richest at the time. In 1565 a coalition of Muslim sultanates defeated the Vijayanagara Empire, its capital was conquered and destroyed, and the city was left in ruins. Hampi remains a religious centre, with the active Virupaksha Temple at its heart.