What mathematical symbol can be put between 5 and 9, to get a number bigger than 5 and smaller than 9?

It's a test that will check your IQ.

Suppose you have one 11 minute hourglass and one 13 minute hourglass.

Can you measure exactly fifteen minutes using them ?

Can you count the number of blocks in the picture below?

What do you see in the image below

What does this rebus mean?

O
N
C
E
TIME

How many triangles can you find in this given picture?

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

If I put in one canary per cage, I have one bird too many. If I put in two canaries per cage, I have one cage too many. How many cages and canaries do I have?

What is the fewest number of coins that would be required in order to make sure each and every coin touches exactly three other coins?

I came first on earth but second on the heaven.
I also came twice in a week but found just once in a year.
I stay away from months but you can find me in February.

What am I?