Before Mount Everest was discovered, what was the highest mountain in the world?

I am the fastest animal but cannot climb the tree. What am I?

A man dies of old age on his 25 birthday. How is this possible?

A father's child, a mother's child, yet no one's son.

Who am I?

How can you make number one disappear by adding something to it?

A maths symbol is hidden in the below Bar Graph. Can you decipher it?

Assume the given figure to be a delicious doughnut. Yes, now you can concentrate more on the puzzle. So you have this delicious doughnut in your refrigerator when your friends come knocking at the door. There are eight of them. Now you have to make three cuts in this doughnut so that each one of you nine people can enjoy a piece of it. Neither you nor your friends would mind the size of their piece as long as they are getting it. How will you do it?

Which five letter word can be added at the end of below word to form a
valid word?

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A Shopkeeper collects 71 rupees in the form of 20 paisa and 25 paisa.
He collects a total of 324 coins.

Can you tell me how many number of 20-paisa and 25-paisa he got?

Nine marbles are arranged in the image below. Can you slide two marbles to form a square?