Quickly Solve this riddle

7 - 4 + 3 * 0 + 1 = ?

The square root of number 121 is "11". What is the square root of the number "12345678987654321."?

Two guards were guarding the camp.Guard-1 was looking towards the south to make sure no threat is coming from the road.Guard-2 was looking at the north to make sure no threat is coming from the top. Suddenly Guard-1 ask the Guard-2 why he is smiling?How Guard-1 knows that Guard-2 is smiling?

What occurs twice in a week, once in a year but never in a day?

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.

A man was found murdered on Sunday morning. His wife immediately called the police. The police questioned the wife and staff and got these alibis: The Wife said she was sleeping. The Cook was cooking breakfast. The Gardener was picking vegetables. The Maid was getting the mail. The Butler was cleaning the closet. The police instantly arrested the murderer. Who did it and how did they know?

They are three errirs in this question. Can you find them?

Find the next number in the series?
2, 12, 36, 80, 150, 252, 392, _ ?

What number does the below three word/phrase identify and why?
1. Deck
2. Year
3. Singing in the Rain

In the picture that is attached with this question, you can find a square which comprises of four little squares inside it. Consider this square to be made with matchsticks. You have to remove two matchsticks such that only two squares remain instead of five.How will you do it ?