If eleven plus two equals one, what does nine plus five equal?

You see a boat filled with people, yet there isn’t a single person on board. How is that possible?

I am a prime number.
The double of myself is equal to the square of me.

which number am I?

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

Find the number of squares in the below picture

Can you find the missing piece of the Porsche?

Most people think of me as money. But when they find me in the water, they won’t get any money out of me. What am I?

Nine marbles are arranged in the image below. Can you slide two marbles to form a square?

On a special event at the prison, 5 prisoners John, Jacob, Krist, Tang, and Dang given a chance to go to a sauna and can bring one thing with them.

Following are the things that the prisoners bring with them.
John: A soda
Jacob: Thermos
Krist: Book named "How to kill"
Tang: A Walkman
Dang: Harmonica

Since it is a Sauna, no one can see each other. After a while When the steam is switched, Tang was found dead and there was blood all around.
J Bond was called and he instantly come to know who can be the murderer. How?

When I get multiplied by any number, the sum of the figures in the product is always me. What am I?