Count the squares in the matchstick puzzle below?

How many times do a clock's hands overlap in a day ?

There are 20 people in an empty, square room. Each person has full sight of the entire room and everyone in it without turning his head or body, or moving in any way (other than the eyes). Where can you place an apple so that all but one person can see it?

If you had a pizza with crust thickness 'a' and radius 'z', what's the volume of the pizza?

How can you spell "White of an egg" in one word?
Hint: I know you can spell coke, poke, and joke.

Using four sevens (7) and a one (1) create the number 100. Except for the five numerals, you can use the usual mathematical operations (+, -, x, :), root and brackets ()

Can you decipher these quotes by Albert Einstein?
Blf xzm mvevi hloev z kilyovn lm gsv ovevo lm dsrxs rg dzh xivzgvw.

You can hear me, but you can't touch or see me.

What am I?

If 21x = 79x, what is the value of x?

what does the below rebus means?