What is both possible and impossible at the same time?

A famous swimmer can swim downstream in a lake in exactly 40 minutes with the lake current.
He can swim upstream in that lake in exactly 60 minutes against the lake current.
The length of the lake is 2 km.

How long he can cover the distance of one side at a still lake with no current?

What is the Surname of Barbie Doll?

In a science lab, a petri dish hosts a healthy colony of yeast for an experiment. Now every minute, all the yeast cells divide into two. At noon, there was just a single cell of yeast and at 1:22, the Petri dish was half full. Can you calculate when the dish will be full of yeast?

Move four matchsticks to the below square to form three squares?

Always in you, Sometimes on you;

If I surround you, I can kill you.

What am I?

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

I can write cow in 13 letters.

Can You?

You’ll find me on Mercury, Earth, Mars, Jupiter, Saturn, and Uranus. But never Neptune, or Venus. What am I?

f you were running a race, and you passed the person in 2nd place, what place would you be in now?