How many times can you subtract the number two from the number fifty?

If I remove one from eleven it becomes Ten and if I remove one from nine also becomes Ten. How?

I am a type of vehicle that has two wheels and is powered by humans. What am I?
Hint 1: You can ride me for exercise.
Hint 2: I am environment-friendly.

Two in a corner, one in a room, zero in a house, but one in a shelter. What is it?

The first two letters signify a male, the first three letters signify a female, the first four letters signify a great, while the entire world signifies a great woman. What is the word?

Can you name any English verb that becomes its past tense by simply rearranging the alphabets ?

What has one letter and starts with an E?

Can you spot what's wrong with the following sentence?

PETER WAS ANGRY AT
HIMSELF BECAUSE HE
ACCIDENTALLY LEFT THE
THE KEYS TO HIS CAR
AT HIS FRIEND'S HOUSE.

What has six faces, but does not wear makeup, has twenty-one eyes, but cannot see?

I am taken from a mine and shut up in a wooden case, from which I am never released, and yet I am used by almost every person. What am I?