Can you place six X (crosses) in below board without making three in a row in any way ?

If nine thousand, nine hundred nine dollars is written as $9,909,
how should twelve thousand, twelve hundred twelve dollars be written?

If we tell you that there is a relation between the numbers and letters in the given figure, can you analyze it and find the missing letter in the last box?

13 decks of cards have been mixed. What is the minimum number of cards that must be taken out from the above-mixed cards to guarantee at least one 'four of a kind?

If I remove one from eleven it becomes Ten and if I remove one from nine also becomes Ten. How?

I am not a bull but I have horns.
I am not an ass but I have a pack saddle.
Wherever I go, I leave silver behind me.

Who am I?

If we add four times the age of John four years from now to five times his age five years from now we get ten times his current age.

How old will John be two years from now?

How many sides does a circle have?

Can you find the key in the picture below?

They came out at night, without being called.
They lost at day, without being stolen.
Who are they?