How many sides does a circle have?

You’re out on the water and see a boat filled with people. You look away for a second and look back again, but this time you don’t see a single person on the boat. Why? Hint: The boat did not sink.

A tree doubled in height each year until it reached its maximum height over the course of ten years. How many years did it take for the tree to reach half its maximum height?

There are 2 people near the river and both of them want to get on the other side. The boat can only take one of them. But they got across.
How?

John and Jill are madly in love with each other. To remind Jill of his pure love, John wants to send her a ring by post but in their country where burglary is quite prominent, any package that is not locked comes under the risk of being stolen for the contents.

John and Jill possess many padlocks but neither one of them has the other key.

Can you find a way John can send the ring to Jill safely?

There’s a girl who has a large family. She has an equal amount of brothers and sisters, but each brother only has half as many brothers and sisters. What’s the correct amount of brothers and sisters?

Which statement is true out of the following?
One statement here is false.
Two statements here are false.
Three statements here are false.

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 a Boat in the mid of a river. You have two cigarettes with you. One of these two you have to light, how will you light the cigarette?

Find the next number in the series?
2, 12, 36, 80, 150, 252, 392, _ ?