What is the fastest way to double your money?

How do you go from 98 to 720 using just one letter?

If you remove one from eleven, it becomes ten. If you remove one from nine, it becomes ten.

How is this possible?

How many points are there on the globe where, by walking one mile south, then one mile east and then one mile north, you would reach the place where you started?

How many triangles are there on the puzzle below?

Which English verb becomes past tense just by rearranging the letters?

I never stop running even when I standstill. If I am formed by joining two identical bodies together, can you guess who I am?

Complete the table series riddle by finding the number that can replace "??".

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?

It can't be seen, can't be felt, can't be heard, and can't be smelt.
It lies behind stars and under hills, And empty holes it fills.
It comes first and follows after, Ends life, and kills laughter.
What is it?