Why Aeroplane windows are round?

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

You are on your way to visit your Friend, who lives at the end of the hill. It is his birthday, and you want to give him the cakes you have made. Between your house and his house, you have to cross 5 bridges, and as it goes in the land of make believe, there is a troll under every bridge! Each troll, quite rightly, insists that you pay a troll toll. Before you can cross their bridge, you have to give them half of the cakes you are carrying, but as they are kind trolls, they each give you back a single cake. How many cakes do you have to leave home to make sure that you arrive at a friend's house with exactly two

I am a type of vehicle that has two wheels and is powered by humans. What am I?
Hint 1: You can ride me for exercise.
Hint 2: I am environment-friendly.

If your uncle’s sister is not your aunt, what relation is she to you?

I guess 76.8% of readers will like this riddle.

What's the least number of people should read this post?

How many triangles can you count in the figure given?

The peacock is a bird that does not lay eggs. How do they get baby peacocks?

What does does this rebus picture means ?

John has played 50 ODI's and his average is 50. How many runs should he score in his 51st ODI, so that his average score jumps to 51?