What has no start, end, or centre?

A man has a barrel filled with oil that weighs 100 pounds, and then he puts something into it. Now the barrel weighs less than 100 pounds. What did he put in the barrel?

What occurs twice in a week, once in a year but never in a day?

What jumps when it walks and sits when it stands?

What number does the below three word/phrase identify and why?
1. Deck
2. Year
3. Singing in the Rain

What is the value of 1/2 of 2/3 of 3/4 of 4/5 of 5/6 of 6/7 of 7/8 of 8/9 of 9/10 of 1000?

Cristina leaves home and then she makes exactly 3 left turns and returns home where she found 2 girls wearing the mask.

Who are these two masked girls?

I throw two dice simultaneously.

What is the probability of getting a sum as 9 of the two numbers shown?

I have no doors but I have keys, I have no rooms but I have space, you can enter but you can’t leave! What am I?

A rubber ball keeps on bouncing back to 2/3 of the height from which it is dropped. Can you calculate the fraction of its original height that the ball will bounce after it is dropped and it has bounced four times without any hindrance ?