Replace the question mark with the correct number.

Can you find the next number in the below sequence
3 , 7 , 10 , 11 , 12 , 17 ?

I have no life, but I can die. What am I?

Name a key which is hardest to turn.

In the image below, you can see two glasses and two matchsticks.You need to move four matchsticks in such a manner that the crosses come inside the glasses. Note: you cannot move the crossed.

Can you divide the below-given shape into four equal and identical pieces?

John's five friends Rachel, Jacob, Phoebe, Joey and Chandler live on the same road.

Rachel lives in the house: A, Jacob lives in the house: B, Phoebe lives in the house: C, Joey lives in the house:D, Chandler lives in the house: E

Mathematically
B*C*D = 1260
B + C + D = 2E
2A = E

The road numbers run from 2 to 222.

Can you tell me the house number of each of John's friends?

What is the next number in this matchsticks series riddle?

Can you find out which number multiplied by itself will give the output as 12345678987654321?

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