Can you solve the below rebus?

By removing one matchstick and adding one matchstick, can you convert the word "ZOO" to an animal name?

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?

There was a blind man. He had four socks in his drawer either black or white. He opened it and took out two socks. Now the probability that it was a pair of white socks is 1/2.

Can you find out the probability that he had taken out a pair of black socks ?

Andrew sees a very rare bird named "Ruppell's vulture". Soon Andrew was dead. Can you explain the mystery, Mr. Sherlock?

What is the riddle which can be asked all day with a different correct answer each time.

You are trapped in a room with two doors. One leads to certain death and the other leads to freedom. You don't know which is which.
There are two robots guarding the doors. They will let you choose one door but upon doing so you must go through it.
You can, however, ask one robot one question. The problem is one robot always tells the truth, the other always lies and you don't know which is which.
What is the question you ask?

You and your two friends are working in a multinational company. How can you three find out the average salary of you all without disclosing your own salary to the other two?

You balance a broom horizontally on your finger such that your finger is present at the centre of the gravity of the broom (precisely). You mark the spot and cut the broom into two halves. You are left with two pieces - one long piece with the handle and one short piece with bristles and a portion of the handle.

If you weigh both the pieces now, what will happen?
a) The longer piece weighs more.
b) The shorter piece weighs more.
c) Both pieces weigh equally.

Replace the question mark with the correct number, given the pair of numbers exhibits a similar relationship?

? : 3839 :: 11 : 1209