How many sides does a circle have?

A Scientist was fifty years old in the year 2000 but he was forty years old in the year 2010. How can this be possible?

PS: It has a logical answer.

I have four wings but can't fly.
I express no emotions.
I am found on the exact spot every time you look.
I keep toiling away with a little sound.

Do you know what am I?

Identify the 10 differences between the two given pictures.

Which three-digit number, made of consecutive digits, like 567, is 2 less than a cube and 2 more than a square?

What part of the chicken has the most feathers?

Sherlock Holmes was challenged to make a pre-drawn line smaller without erasing it. He did it in fractions of seconds. How?

Do You See It?

I have no doors but I have keys, I have no rooms but I have space, you can enter but you can’t leave! What am I?

A girl was standing near the window thinking something. All of a sudden she decides something and throws something out of the window. She dies very soon after throwing it. She was perfectly healthy and had no disease or allergy. No one killed her and she did not commit suicide.

Can you think of any possible explanation that is logical as well for what happened there?