What is black when you buy it, red when you use it, and gray when you throw it away?

It's a 7-letter word.
If we remove 1 letter from it, it remains the same.
If we remove 2 letters from it, it remains the same.
If we remove 3 letters from it, it remains the same.
If we remove all the letters from it, still it remains the same.
What is it?

You walk into a room where there are three primates held in their respective cages:
1) A lion who is eating the flesh of a goat.
2) An orangutan who is playing with blocks.
3) A donkey who is sitting idle.

Who is the most intelligent primate in the room?

Decode below three cipher riddles:

26 L of the A
7 D of the W
1000 Y in a M

I am the black child of a white father, a wingless bird, flying even to the clouds of heaven. I give birth to tears of mourning in pupils that meet me, even though there is no cause for grief, and at once on my birth, I am dissolved into air. What am I?

In 1990, a person is 15 years old. In 1995, that same person is 10 years old. How can this be?

Can you find out the missing number in the grid?

You can hear me, but you can't touch or see me.

What am I?

Can it be possible to build a house that has all its four walls facing towards the South?

What number when divided in half becomes zero?