Can you find a pattern and the missing number in the series given below?

100, 155, 258,? , 584, 819.

A man stands on one side of a river, his dog on the other. The man calls his dog, who immediately crosses the river without getting wet and without using a bridge or a boat. How did the dog do it?

Where do fish keep their money?

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.

You need to move three matchsticks to form three squares. Can you do it?

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

We have four gears with below features=> Both Gear A and D has 60 teeth=> Gear B has 40 teeth=> Gear C has 20 teeth=> Every two minutes, Gear B makes 25 full turns.What is the relative speed of Gear A and Gear B?

John can place six large boxes or nine small boxes into a carton.

Can you find out in how many cartons can he place sixty-six boxes in total?

What does this simple rebus mean?

Can you decipher the following common phrase?

T M C
A U O
H S M
W T E