You can take four of the five letters out of this word, but the pronunciation never changes. What is the word?

Twice ten are six of us,

Six are but three of us,

Nine are but four of us;

What can we possibly be?

Would you know more of us?

Twelve are but six of us,

Five are but four, do you see?

What are we?

We have two identical balls in terms of diameter and weight. However, one of them is solid and the other is hollow.

Without knocking the ball, can you find the solid ball?

John enters a small room. The Door Closes.
When the door opens, John is in a larger room.

Explain?

A 3 digit number is such that it's unit digit is equal to the product of the other two digits which are prime. Also, the difference between it's reverse and itself is 396.

What is the sum of the three digits?

Assume there are approximately 5,000,000,000 (5 billion) people on Earth. What would you estimate to be the result, if you multiply together the number of fingers on every person's left hand? (For the purposes of this exercise, thumbs count as fingers, for five fingers per hand.) If you cannot estimate the number then try to guess how long the number would be.

Consider all the numbers between 1 and 1 million. Among all these numbers, there is something very special about the number 8 and the number 2202. What is it?

Can you make the number 24 by utilizing the numbers 1, 3, 4 and 6? You must use one number only one time and you can use mathematical operation symbols anytime anywhere.

What breaks yet never falls, and what falls yet never breaks?

When monkey rotate the gear, which mark will be hit 1 or 2 ?