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

In a concert, Christina is performing a dance show with her group.
At 10:00, she and her crew were dancing in an absolutely straight line. At that time Christina was standing in 4th position from both the front and back end of the row.

What was the size of her crew?

John is looking at Jenifer, but Jenifer is looking at Jacob. John is married, but Jacob is not.

Is a married person looking at an unmarried person ?

Can it be possible to build a house that has all its four walls facing towards the South?

A man says, "Brothers and sisters, have I none, but that man's father is my father's son." Who is that man?

Different lights make me strange by changing me into different sizes. What am I?

In a contest, four fruits (an apple, a banana, an orange, and a pear) have been placed in four closed boxes (one fruit per box). People may guess which fruit is in which box. 123 people participate in the contest. When the boxes are opened, it turns out that 43 people have guessed none of the fruits correctly, 39 people have guessed one fruit correctly, and 31 people have guessed two fruits correctly.
How many people have guessed three fruits correctly, and how many people have guessed four fruits correctly

What number does the below three word/phrase identify and why?
1. Deck
2. Year
3. Singing in the Rain

Take away my first letter, then take away my second letter. Then take away the rest of my letters, yet I remain the same. What am I?

What has 88 keys?