Can you find out which number multiplied by itself will give the output as 12345678987654321?

How many times can you subtract the number two from the number fifty?

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?

In the Chess Board picture below white army is arranged. You need to add a black army on the board such that no piece is under any threat.
Note: Army comprised of 1 king, 1 queen, 2 rooks, 2 bishops, 2 knights, and 8 pawns.

Place the numbers from 1 to 9 in the circles in a manner that each side of the triangle sums up to 17.

If an electric train is travelling south, then which way is the smoke going?

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

I am the first thing you need while camping.
I am always with the person named Marcos Valencia and Carrick.
But Pogba Zlatan and Rooney think I am wasteful and do not need me.
I am the second to the last thing to add when you are making a patch.

What am I?

There once were seven dwarfs who were all brothers. They were all born two years apart. The youngest dwarf is seven years old. How old is his oldest brother?

Before Mount Everest was discovered, what was the highest mountain in the world?