The square root of number 121 is "11". What is the square root of the number "12345678987654321."?

There are people and strange monkeys on this island, and you can not tell who is who (Edit: until you understand what they said - see below). They speak either only the truth or only lies.
Who are the following two guys?
A: B is a lying monkey. I am human.
B: A is telling the truth.

If you read clockwise, you can form a word by inserting three missing letters in the picture given below. Can you do it?

Find the next number in the series

12, 20, 40, 72, 116, 172 ?

If,

20 % 5 = 24

21 % 7 = 33

42 % 6 = 67

Then;

66 % 6 = ?

Replace the question mark with the correct number in below Picture:

What work can one never finish?

I always drive my customer away.

Who am I?

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

A man calls his dog from the opposite side of a river. The dog crosses the river without a bridge or a boat and manages to not get wet. How is this possible?