Can you replace the question mark with the correct letter?

6 + 6 + 6 = N
7 + 7 + 7 = E
8 + 8 + 8 = R
0 + 0 + 0 = ?

What does this below rebus puzzle mean?

What do you think with the below Picture ?

I am a seven-letter word but if you remove four of my letters I will have one left. What word am I?

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.

Complete the series by replacing "?" with the correct number.

ST ND RD TH '?'

Which tank will fill first?

There were three women in all the swimming costumes!
One was happy and the other two were sad!
The happy one was crying and the sad ones were smiling.
Why was this?

Can you move 2 matchsticks to form four equal sized squares.

How many letters are in the alphabet?