Why Aeroplane windows are round?

Use the digits from 1 up to 9 and make 100.

Follow the rules.
=> Each digit should be used only once.
=> You can only use addition.
=> For making a number, two single digits can be combined (for example, 4 and 2 can be combined to form 42 or 24)
=> A fraction can also be made by combining the two single digits (for example, 4 and 2 can be combined to form 4/2 or 2/4)

Question: how can we do this?

Count the number of triangles in the below picture?

What is so fragile that saying its name breaks it?

You need to complete the maze by entering from the entrance marked below in the figure near the yellow circle, bottom left and leaving from the exit point near the green circle, bottom middle.

Rule of Game: You can move only by exchanging green and yellow circles.

A boy was at a carnival and went to a booth where a man said to the boy, "If I write your exact weight on this piece of paper then you have to give me $50, but if I cannot, I will pay you $50." The boy looked around and saw no scale so he agrees, thinking no matter what the carny writes he'll just say he weighs more or less. In the end the boy ended up paying the man $50. How did the man win the bet?

A word I know has six letters it contains, remove one letter and 12 remain. What is it?

O_er_t_o_

Complete the missing letters of the given word.

Is the statement valid that it does not matter how much older a sibling is, eventually the younger one will be half as old as the older one?

Many have heard it, but nobody has ever seen it, and it will not speak back until spoken to. What is it?