Always in you, Sometimes on you;

If I surround you, I can kill you.

What am I?

Below is the sum of symbols in each row and column in the figure. Analyzing the figure, can you find out the value of the symbols?

Take one out and scratch my head, I am now black but once was red. What am I?

Find three numbers such that

* When we multiply three numbers, we will get the prime numbers.
* The difference between the second and the first number is equal to the third and second.

Can you find the dog hidden in a group of pandas?

A seven-year-old kid challenged his classmates that he can make the number one disappear by adding something to it.

How can he do that?

What is both possible and impossible at the same time?

I am a three digit number.
My tens digit is five more than my ones digit.
My hundreds digit is eight less than my tens digit.
What number am I?

Which tank will fill first?

Place a mathematical symbol between the numerals 5 and 9 in such a way that the resulting number is greater than 5 but smaller than 9.