The last person took the basket with the last egg still inside.

Light both the ends of the first string and one end of the second string.
30 minutes will have passed when the first string is fully burned,
which means 30 minutes have burned off, while on the second string
light the end of the second string and when it is fully burned, 45 minutes will have passed.

Mary.

Mary’s mothers fourth child was Mary herself.

3

Socks do not come in in left and right, so any black will pair with any other black and any white will pair with any other white. If you have three socks and they are either colored black or white, then you will have at least two socks of the same color, giving you one matching pair.

28

Each day he makes it up another meter, and then on the twenty seventh day he can leap three meters and climb out.

The two triangles have different slopes so in the second shape the two triangles cause the shape to bulge out to account for the extra square unit.

Tip the glass of water until the water reaches the rim of the glass and if the water lines up perfectly with the bottom rim of the glass, it is half full.

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Start both hourglasses then when the 11 minute hourglass has finished immediately flip it again. When the 13 minute hourglass runs out the 11 minute hourglass will have 9 minutes left, so flip it and it will last another 2 minutes, 13 minutes + 2 minutes = 15 minutes.