The square root of number 121 is "11". What is the square root of the number "12345678987654321."?

Can you count the number of triangles in the given picture?

In the city of Brain Teasers, 5% of people do not list their phone numbers. Now if we select random 100 people from the phone directory, then how many people selected will have unlisted phone numbers?

How high do you have to count before you use the letter “a” in the English spelling of the whole number?

Is the statement valid that it does not matter how much older a sibling is, eventually the younger one will be half as old as the older one?

Why is a river so rich ?

What can you catch but never throw?

The answer I give is yes, but what I mean is no. What was the question?

I am the beginning of the end, and the end of time and space. I am essential to creation, and I surround every place. What am I?

There was once a college that offered a class on probability applied to the real world. The class was relatively easy, but there was a catch. There were no homework assignments or tests, but there was a final exam that would have only one question on it. When everyone received the test paper it was a blank sheet of paper with a solitary question on it: 'What is the risk?'.Most students were able to pass, but only one student received 100% for the class! Even stranger was that he only wrote down one word!
What did he write?