There is an English word that can be used up to four times in a row without modifying the spelling and form a valid grammatical sentence.

Do you know what word is that?

If 5 cats catch 5 mice in 5 minutes, how long will it take one cat to catch a mouse?

A Scientist was fifty years old in the year 2000 but he was forty years old in the year 2010. How can this be possible?

PS: It has a logical answer.

I am a word that begins with the letter “i.” If you add the letter “a” to me, I become a new word with a different meaning, but that sounds exactly the same. What word am I?

What can go up a chimney down, but can’t go down a chimney up?

81 x 9 = 801. What must you do to make the this equation true?

No matter how little or how much you use me, you change me every month. What am I?

A tree doubled in height each year until it reached its maximum height over the course of ten years. How many years did it take for the tree to reach half its maximum height?

A thief enters a store and threatens the clerk, forcing her to open the safe. The clerk says, “The code for the safe is different every day, and if you hurt me you’ll never get the code.” But the thief manages to guess the code on his own. How did he do it?

Double it and multiply it by 4. Then divide it by 8 and you’ll have it once more. What number is it?