You may enter, but you may not come in. I have space, but no room. I have keys, but open no lock. What am I?

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?

I am a prime number.
The double of myself is equal to the square of me.

which number am I?

Which Travels Faster? Solve below famous picture riddle:

Can you name an animal whose killing cannot be performed without spilling your own blood?

Can you find the odd number in the following?

2716, 4135, 5321 and 7145

How will you measure 15 minutes using two hourglasses of 7 minutes and 11 minutes respectively?

How can you spell "White of an egg" in one word?
Hint: I know you can spell coke, poke, and joke.

Use only one mathematical symbol and all numbers (0-9) to get a sum of 99

What part of the chicken has the most feathers?