Can you replace the question mark with the correct number?

Why is it very easy to weigh a fish?

A deaf and mute man goes to the train station. Tickets for the train are 50 cents each. The man goes to the ticket booth and hands the man inside just a dollar. The man in the booth hands him two tickets.

How did the man in the booth know to give him two tickets without even looking at him?

The person who makes it has no need for it. He who purchases it does not use it. The person who does use it does not know they are. What is it?

What country can make you shiver?

John is 45 years older than his son Jacob. If you find similarities between their ages, both of their ages contain prime numbers as the digits. Also, John's age is the reverse of Jacob's age.

Can you find their ages?

I am weightless, but you can see me. Put me in a bucket, and I'll make it lighter. What am I?

Below, you will find the mathematical proof that 10 equals 9.99999?. But is that possible or there is something wrong about it? Can you find the error?

x = 9.999999...
10x = 99.999999...
10x - x = 90
9x = 90
x = 10

Different lights make me strange by changing me into different sizes. What am I?

Next Number in the Series,

5, 16, 49, 104, ?