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

What is always in front of you but can’t be seen?

There are are five things wrong with this sentence; only geniuses will be able to to spot all of the mitstakes

Can you find out what is missing?

1 3 5
2 4 ?

Hint: It's not six. Think out of the box.

A train full of passengers goes through a tunnel. When the train comes out from the other end, there is no single person on the train.

How did it happen?

Given that

(78)^9 = 6
And (69)^4 = 11

Can you find out

(99)^2 =?

(Note: This is Logical, not Mathematical)

How many times can you subtract the number 5 from 25?

When Jack was six years old he hammered a nail into his favourite tree to mark his height. Ten years later at age sixteen, Jack returned to see how much higher the nail was. If the tree grew by five centimetres each year, how much higher would the nail be?

What is the word or phrase below?
R | E | A | D

Can you count the number of seconds in a year?

Clue: You need to bother about calculation.