A certain street contains 100 buildings. They are numbered from 1 to 100. How many 9's are used in these numbers?

Can you think of any three-dimensional shape that comprises of exactly two surfaces?

I am the black child of a white father, a wingless bird, flying even to the clouds of heaven. I give birth to tears of mourning in pupils that meet me, even though there is no cause for grief, and at once on my birth, I am dissolved into air. What am I?

Three brothers Jacob, John, and James live in Mexico City. The product of the ages of these brothers is 175. Jacob and John are twins. How old is James?

Imagine you are in a room with no windows or doors. How will you get out?

How many words can a pen with half refill write?

The more of this there is, the less you see. What is it?

There is a barrel with no lid and some wine in it. 'This barrel of wine is more than half full,' said Curly. 'No it's not,' says Mo. 'It's less than half full.' Without any measuring implements and without removing any wine from the barrel, how can they easily determine who is correct?

What does man love more than life, hate more than death or mortal strife; That which contented men desire; the poor have, the rich require; the miser spends, the spendthrift saves, and all men carry to their graves?

What is in seasons, seconds, centuries and minutes but not in decades, years or days?