How many words can a pen with half refill write?

What is the fastest way to double your money?

You are a cab driver who pools passengers. You pick 3 people from a destination and drop 1 after an hour. 2 people climb aboard at the same time and you drop 3 at the next destination. After some time, you pick 2 passengers only to drop 1 after a short distance where 3 more passengers climb up the cab. You leave the rest of the passengers one by one to their destination and then come back home.

Can you tell the eye color of the cab driver?

Can you Find and name the hidden bird in the picture below ?

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

Which English verb becomes past tense just by rearranging the letters?

If you remove one from eleven, it becomes ten. If you remove one from nine, it becomes ten.

How is this possible?

I am beautiful, up in the sky. I am magical, yet I cannot fly. To people I bring luck, and to some people, riches. The boy at my end does whatever he wishes. What am I?

Prove that the below maths equation is true.

8 + 8 = 91

What are the next two letters in the following series and why?
W A T N T L I T F S _ _

*Hint: Check Puzzle Title