How can you make number one disappear by adding something to it?

John was running from 40 thieves. John has got 3 gold boxes which weigh as 4kg, 2kg, and 1kg respectively. A witty man asked John to stay with him for seven days in exchange for 1kg gold per day. John needs to stay there for seven days and also do not want to give the witty man any advance. How can John pay for his seven days stay?

There are people and strange monkeys on this island, and you can not tell who is who (Edit: until you understand what they said - see below). They speak either only the truth or only lies.
Who are the following two guys?
A: B is a lying monkey. I am human.
B: A is telling the truth.

Can you make numbers like 24, using numbers 3,3,7 & 7 with any arithmetic operator?

I can write cow in 13 letters.

Can You?

Can you make four (4) nines (9) equal 100?

Find the number of squares in the below picture

500 women soldiers are arranged in an array of ten rows and fifty columns in accordance with their respective heights. Now, the tallest woman from each row is asked to move out in the front. From them, the shortest one is labelled as Alpha. They are then asked to resume their original position.

Now, the shortest woman in each column is asked to come out in front. The tallest among them is labelled as Beta.

Can you find out if Alpha will be taller or Beta?

A certain street contains 100 buildings. They are numbered from 1 to 100. How many 9's are used in these numbers?

With the help clues provided in the image, can you find the 5 digit key?