Be active and find the killer in the picture Riddle below.

Name one eight-letter word with 'kst' in the middle, 'in' the beginning, 'and' at the end.?

The host of a game show, offers the guest a choice of three doors. Behind one is a expensive car, but behind the other two are goats.
After you have chosen one door, he reveals one of the other two doors behind which is a goat (he wouldn't reveal a car).

Now he gives you the chance to switch to the other unrevealed door or stay at your initial choice. You will then get what is behind that door.

You cannot hear the goats from behind the doors, or in any way know which door has the prize.

Should you stay, or switch, or doesn't it matter?

A professor thinks of two consecutive numbers between 1 and 10.
'A' knows the 1st number and 'B' knows the second number

A: I do not know your number.
B: Nor do I know your number.
A: Now I know.

What are the four solutions for this?

Can it be possible to build a house that has all its four walls facing towards the South?

How many words can a pen with half refill write?

What is full of holes but still holds water?

Can you place six matchsticks in a manner that each of the matchsticks is in touch with the other five matchsticks?

On one occasion, A Boy collects 71 rupees in form of 20 paise and 25 paise. He collects a total of 324 coins.

Can you tell me how many 20-paisa and 25-paisa he got?

Replace the question mark in the picture below.