Can you replace the question mark with the correct letter?

6 + 6 + 6 = N
7 + 7 + 7 = E
8 + 8 + 8 = R
0 + 0 + 0 = ?

The host of a game show offers the guest a choice of three doors. Behind one is an expensive car, but behind the other two are goats.
After you have chosen one door, he reveals one of the other two doors behind which is a goat (he wouldn't reveal a car).

Now he gives you the chance to switch to the other unrevealed door or stay at your initial choice. You will then get what is behind that door.

You cannot hear the goats from behind the doors, or in any way know which door has the prize.

Should you stay, or switch, or doesn't it matter?

Twice ten are six of us,

Six are but three of us,

Nine are but four of us;

What can we possibly be?

Would you know more of us?

Twelve are but six of us,

Five are but four, do you see?

What are we?

We have shown you a regular water barrel as below. Without using any measuring device can you check if the barrel is more than half-filled or less than half-filled?

Complete the following series. It.s very logical:

1, 4, 5, 6, 7, 9, 11, __?

what's the probability of getting a king or a queen from a pack of 52 cards?

There's one "sport" in which neither the spectators nor the participants know the score or the leader until the contest ends.

What is it?

Spot the cat in the picture below

Take away my first letter, then take away my second letter. Then take away the rest of my letters, yet I remain the same. What am I?

Count the number of triangles in the below picture?