Can you count the number of triangles in the picture below?

What is the next number?

77, 49, 36, 18 ?

You board a train. The train will have to enter a tunnel soon. You are claustrophobic. Which place is the best for you to sit?

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?

Complete the series by replacing "?" with the correct number.

ST ND RD TH '?'

What word is represented by this rebus?

I am thinking of a five-digit number such that:
The first and last digits are the same, their submission is an even number and multiplication is an odd number and is equal to the fourth number. Subtract five from it and we obtain the second number. Then divide into exact halves and we get the 3rd number.

What number I am thinking of?

In a football game, Christina defeated Teresa by 2 - 0 but no man from either side scored. How can this be possible?

I am sure no one can have two things for dinner. what are they?

Below, you will find the mathematical proof that 10 equals 9.99999?. But is that possible or there is something wrong about it? Can you find the error?

x = 9.999999...
10x = 99.999999...
10x - x = 90
9x = 90
x = 10