How many words can a pen with half refill write?

In Greek mythology, the Sphinx sat outside of Thebes and asked this riddle of all travellers who passed by. If the traveller failed to solve the riddle, then the Sphinx killed him/her. And if the traveller answered the riddle correctly, then the Sphinx would destroy herself. The riddle:

What goes on four legs in the morning, on two legs at noon, and on three legs in the evening?

Oedipus solved the riddle, and the Sphinx destroyed herself.

You can see it everyday, But cannot touch it at will. What is it?

10+10 and 11+11 can give you the same answer.

Explain how?

If your uncle’s sister is not your aunt, what relation is she to you?

If 5 cats catch 5 mice in 5 minutes, how long will it take one cat to catch a mouse?

You are playing a game with your friend Jack. There are digits from 1 to 9. You both will take turn erasing one digit and adding it to your score. The first one to score 15 points will win the game.

Would you want to play first or second?

PS: The sum should be exactly 15.

Eight of us go fourth, not back, to protect our king from an attack. What are we?

Solve below popular number sequence
314 159 265 358 979 323 846 ?

The person who makes it has no need for it; the person who buys it has no use for it. The person who uses it can neither see nor feel it. What is it?