Find The Next Number In The Sequence

30 10 15 13 0 16 -15 ?

What does this mathematical rebus means ?

What is the centre of gravity?

I am first found in caves, now prolific online; I am a depiction, a drawing, a symbol, or sign. I will convey whichever mood you could wish; or for that matter, a fist, flask, or fish. What am I?

Outside a massage parlour, there is a board that reads
"I only massage those who do not massage themselves."

Reading the above statement, does the masseur massage himself?

What number do you get when you multiply all of the numbers on a telephone's number pad?

There is a unique number which when multiplied by any number from 1 to 6, we will get the new number that contains the same digits only.

Can you find that number?

What has to be broken before you can use it?

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

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

What is the largest amount of money that you can possess in change and still if someone asks you for a dollar, you won't be able to give?