What work can one never finish?

A train full of passengers goes through a tunnel. When the train comes out from the other end, there is no single person on the train.

How did it happen?

In this image, you can see three almost identical Doraemon images. Can you spot the odd one out from them?

Can you solve this tricky maths equation problem by replacing it? mark with the correct symbol?

19834 -----: 187
15921 -----: 153
17561 -----: 139
13734 -----: ???

Move three sticks of the spiral below to form a square.

Identify The phrase in the picture.

Replace the question mark with the correct number below.

John was working on a Chemical Mixture whose weight comprise 90% liquid and 10% solid. The total weight of the mixture is 20 pounds. After a while, John noticed that some of the liquid evaporated and now the liquid comprises just 50% of the weight.

What is the weight of the chemical mixture now?

It comprises roots which nobody sees,
Much taller than those trees,
Up and up it goes,
Still it never grows?

It has a long neck, A name of a bird, Feeds on cargo of ships, It's not alive,

What is it?