Complete the table series riddle by finding the number that can replace "??".

A 52% bias toss for head using the 51% tail bias coin was done to obtain a fair result.

Can you find how bias is the floor in this case?

We have shown you a regular water barrel as below. Without using any measuring device can you check if the barrel is more than half-filled or less than half-filled?

In which direction should the missing arrow point?

What can you serve, but never eat?

If you're 8 feet away from a door and with each move you advance half the distance to the door. How many moves will it take to reach the door?

What is the end of everything?

I add 5 to 9 and get 2. The answer is correct, so what am I?

Accidentally, two trains are running in the opposite direction and enter a tunnel that is 200 miles long. A supersonic bird that has fled the lab and taken shelter in the tunnel starts flying from one train towards the other at a speed of 1000 mph. As soon as it reaches the second train, he starts flying back to avoid collision and meets the first train again at the other end. The bird keeps flying to and fro till the trains collide with each other.

What is the total distance that the supersonic bird has traveled till the trains collided?

The following sentence is false. The preceding sentence is true.
Are these two sentences true or false?