What's the only room from which no one can enter or leave

Why do we preferably have round manhole covers and not square ones?

How many words can a pen with half refill write?

I have an eye but still cannot see.

Who am I?

Can you decipher the following common phrase?

T M C
A U O
H S M
W T E

During which month do people sleep the least?

81 x 9 = 801. What must you do to make the this equation true?

I want to fill my bucket using both cold and hot water.
I have two taps for both cold and hot water. The hot water tap fills the bucket in exact 6 hours and the cold water tap fills the bucket in exact 4 hours.
I turn both of them simultaneously but I forgot to turn off another tap which removes the water out of the bucket. This tap can empty the bucket in 12 hours.

How Long will it take to fill the bucket?

Your job is to measure 45 minutes if you have only two cords and matches to light the cords.

1. The two cords are twisted from various materials, so their different segments can burn at different rates.
2. Each cord burns from end to end in exactly one hour.

Describe your way of measuring the 45 minutes.

There is a place where if I stand up straight, I will still be considered sideways.