How many sides does a circle have?

I hide my treasure in the ground, my tail is big and fluffy. If you spot me in a tree, please don’t call me scruffy. What am I?

Find a 9-digit number, which you will gradually round off starting with units, then tenth, hundred etc., until you get to the last numeral, which you do not round off. The rounding alternates (up, down, up ...). After rounding off 8 times, the final number is 500000000. The original number is commensurable by 6 and 7, all the numbers from 1 to 9 are used, and after rounding four times the sum of the not rounded numerals equals 24.

I look flat, but I am deep. Hidden realms I shelter. Lives I take, but the food I offer. At times I am beautiful. I can be calm, angry, and turbulent. I have no heart but offer pleasure as well as death. No man can own me, yet I encompass what all men must have. What am I?

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

Why is it very easy to weigh a fish?

2, 3, 5, 9, 17, _ What is the next number in the sequence?

By removing one matchstick and adding one matchstick, can you convert the word "ZOO" to an animal name?

Remove two matchsticks to make the below equation correct.

What can run but never walk, have a mouth that never speaks, have a head that never weeps, and have a bed but never sleeps?