Can you think of any three-dimensional shape that comprises of exactly two surfaces?

Can you place three balls such that the equation shown in the picture holds true?

Eight of us go fourth, not back, to protect our king from an attack. What are we?

My thunder comes before the lightning; my lightning comes before clouds; my rain dries all the land it touches. What am I?

The first person saw the bridge step on it and crossed,
the second person saw the bridge did not step on it but crossed,
the third person did not see the bridge did not step on it but crossed.
Who are these people?

You see me once in June, twice in November, and not at all in May. What am I?

Assume there are approximately 5,000,000,000 (5 billion) people on Earth. What would you estimate to be the result, if you multiply together the number of fingers on every person's left hand? (For the purposes of this exercise, thumbs count as fingers, for five fingers per hand.) If you cannot estimate the number then try to guess how long the number would be.

I am a five-letter word and people eat me. If you remove the first letter I become an energy form. If you remove the first two letters, I am needed to live. Scramble the last three letters and I am a drink. What word am I?

O_er_t_o_

Complete the missing letters of the given word.

My grandson is about as many days as my son in weeks, and my grandson is as many months as I am in years. My grandson, my son and I together are 120 years. Can you tell me my age in years ?