When I get multiplied by any number, the sum of the figures in the product is always me. What am I?

If 5 cats catch 5 mice in 5 minutes, how long will it take one cat to catch a mouse?

What has many keys but can’t open a single lock?

How many letters are in the alphabet?

You Throw The Outside, Cook The Inside
Eat The Outside, Throw The Inside.

What Is It?

How many sides does a circle have?

Begin with a word, five letters to my name,
Remove the first and last but I am the same
Take out my middle and still, I remain.
What word am I?

I am white when I am dirty, and black when I am clean. What am I?

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?

I am looking for a word that change both gender and number when i add the letter 'S'.

What Word am I Looking For ?