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

There is a box full of marbles,
all but two are blue,
all but two are green,
and all but two are red.

How many marbles are in the box?

How many pluses should we put between the digits of 987654321 to get a total of 99, and where?

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?

Is the statement valid that it does not matter how much older a sibling is, eventually the younger one will be half as old as the older one?

John was visiting his friend Jacob. He found out that his friend's wife had just killed a burglar in self-defense.
John asks Jacob about what happened and he told that "His wife was watching television when suddenly the bell rang. She thought that it is her husband Jacob but she found the burglar who attacked her instantly and she got so frightened that she killed the burglar immediately with the knife.
John asked the police to arrest his friend's wife. Why?

Can you solve this amazing hard number series problem?
7, 8, 10, 12, 16, 18 ?

If eleven plus two equals one, what does nine plus five equal?

Which is Odd One Out and why?

4377

3954

9862

8454

9831

I am a five-letter word and people eat me. If you remove the first letter I become an energy form. If you remove the first two letters, I am needed to live. Scramble the last three letters and I am a drink. What word am I?