– puzzle and solutions ©Alex Bellos (The Guardian)

1) Anna’s father has four daughters. The names of the first three daughters are April, May and June. What’s the name of the fourth daughter?

Solution

Anna, of course! Yes, it’s an old chestnut…

2) Two men marry each other’s mothers. What is the relationship between their sons?

Solution

They are uncle/nephew to each other. This puzzle dates from the eighth century, and is the earliest of this type of kinship riddle.

(I’d also accept the answer posted below the line, which said the relationship would be “quite strained.”)

Let’s call the protagonists Man 1 and Man 2, who have mums Mum 1 and Mum 2. The couples are therefore Man 1 and Mum 2, and Man 2 and Mum 1. If the first couple have Son A, and the second couple have Son B, then Son A is half-brother to Man 2, and thus half-uncle to Son B, who is Man 2’s son. It’s easier to see when drawn as a family tree.

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3) A certain man had great grandchildren, yet none of his grandchildren had any children. How come?

The question talks about great grandchildren, not great-grandchildren. The hyphen makes all the difference. The grandchildren were great, top, brilliant and awesome, but childless.

4) What’s the smallest possible number of people in a family group that contains a grandfather, a grandmother, two fathers, two mothers, four children, three grandchildren, one brother, two sisters, two sons, two daughters, one father-in-law, one mother-in-law and one daughter-in-law?

Solution

Seven. Three siblings (two girls and a boy), their parents, and the father’s parents. Again, it is easier to see when drawn as a family tree.

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5) On one day my friend Olivia has her birthday. Two days later it is the birthday of her elder twin, Oliver. Please explain.

Solution

Oliver was born on March 1 on a plane flying eastwards over the Pacific. A few seconds later the plane crosses the International Date Line, and Olivia is born. She is thus born on February 28, making her the ‘younger’ sister with a calendar birth date one day before her brother’s. On leap years, however, Olivia will celebrate her birthday two calendar days before her older twin.