Why is it very easy to weigh a fish?

A girl was sitting in her hotel room when she heard a knock on the door. She opened the door and found that a man was standing outside.
The man said, "Oh! I am really sorry, I thought this was my room."
He then walked through the corridor to the elevator. The girl did not know the man. She closed her door and called security asking them to apprehend the man.
What made her suspicious of that man? He might have been genuinely mistaken.

Can you find the mistake in the below statement?

Solve The below Equation:

ALFA + BETA + GAMA = DELTA

The Puzzle: A girl, a boy, and a dog start walking down a road.

They start at the same time, from the same point, in the same direction.

The boy walks at 5 km/h, the girl at 6 km/h.

The dog runs from boy to girl and back again with a constant speed of 10 km/h. The dog does not slow down on the turn.
How far does the dog travel in 1 hour?

How can you make the following equation true by drawing only one straight line: 5+5+5=550 ?

When 99 is considered higher than 100?

Can you solve this amazing hard number series problem?
7, 8, 10, 12, 16, 18 ?

Make eight squares by moving only two matchsticks.
Note- Square can be of different sizes.

Until it is measured, not known. Yet how you miss it when it has gone. What is it?