How will you measure 15 minutes using two hourglasses of 7 minutes and 11 minutes respectively?

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

I come in different shapes and sizes.
Parts of me are curved, other parts are straight.
You can put me anywhere you like,
but there is only one right place for me.
What am I?

Count the squares in the matchstick puzzle below?

My friends called me Iron59 because my parents are a chemist and a mathematician. What is my real name?

why number 8549176320 is one of a kind?

A train leaves from point A for point B at 80 mph. After half an hour, another train leaves from point B for point A at 60 mph.

Which of the trains will be farther from point A when they meet ?

What will you call your mother's brother's brother-in-law?

One day Jenifer meets the Lion and the Tiger in the Forest of Forgetfulness. She knows that the Lion lies on Mondays, Tuesdays, and Wednesdays, and tells the truth on the other days of the week. The Tiger, on the other hand, lies on Thursdays, Fridays, and Saturdays, but tells the truth on the other days of the week. Now they make the following statements to Jenifer:

Lion: Yesterday was one of my lying days.

Tiger: Yesterday was one of my lying days too.

What day is it?

What has to be broken before you can use it?