Irene killed hundreds of people mercilessly and yet the police were not able to put her behind the bars. Why?

What common phrase is represented by the below lines

Easy going:
Weak, 'I'm going.'
Tough, 'I'm staying.'

Medium going:
Weak, 'I'm going.'
Tough, 'I'm staying.'

Tough going:
Weak, 'I can't do it, I'm staying!'
Tough, 'Let's get going.'

A detective visits his friend John just to discover that John's neighbour Dr Jacob was murdered. Dr Jacob, who is a mathematician wrote the murderer's name in a code word "Hcqtfz". There were five suspects
1. Ajit
2. Pankaj
3. Ganpat
4. Deenu
5. Hariya

The Detective was instantly able to find the murderer.
Can you?

When my father was 31 I was 8. Now he is twice as old as me. How old am I?

Take 9 from 6, 10 from 9, 50 from 40, and leave 6.

How Come ??

How many minutes are there in Feb 2017?

Note: The shortest answer is the correct answer.

When I go in I might cause pain. I cause you to spit and ask you not to swallow. I can fill your hole. What am I?

All of the flowers I have are orchids except two. All of the flowers I have are hibiscuses except two. All of the flowers I have are roses except two.

Can you tell me how many flowers I have?

Can you tell a 3D object that has just two surfaces?

In the picture, you can see a chess board. On the top left position, the K marks a knight. Now, can you move the knight in a manner that after 63 moves, the knight has been placed at all the squares exactly once excluding the starting square?