What is black when you buy it, red when you use it, and gray when you throw it away?

Always in you, Sometimes on you;

If I surround you, I can kill you.

What am I?

Why Wine Glass Stem is so long?

It comprises roots which nobody sees,
Much taller than those trees,
Up and up it goes,
Still it never grows?

What Time Should the last watch show in the below figure?

Who are the happiest people in IPL match?

How much will a 38° angle measure when looked at under a microscope that magnifies ten times?

Identify the hidden meaning behind this picture?

John drives to his office at 20km/hr. After reaching the office, he realizes that today is a holiday. He went back at an average speed of 30km/hr. Discounting the time spent in the stoppage what was the average speed of his journey?

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?