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

I have teeth but i don't bite. Who Am I ?

What common phrase is represented by the below lines

Easy going:
Weak, 'I'm going.'
Tough, 'I'm staying.'

Medium going:
Weak, 'I'm going.'
Tough, 'I'm staying.'

Tough going:
Weak, 'I can't do it, I'm staying!'
Tough, 'Let's get going.'

Decode below three cipher riddles:

26 L of the A
7 D of the W
1000 Y in a M

What goes up but never comes down?

Why is the Hole below a Lock?

How many Watermelons are there in the below picture?

Mr Red Lives in the red house.
Mr Green Lives in the greenhouse.
Mr Yellow Lives in the yellow house.

Who lives in the Whitehouse?

If nine thousand, nine hundred nine dollars is written as $9,909,
how should twelve thousand, twelve hundred twelve dollars be written?

The centre of the third figure is empty. What digit should fit inside?