What word begins and ends with an E, but has only one letter?

How can you write nineteen in a manner that if we take out one, it becomes twenty?

Can you spot what's wrong with the following sentence?

PETER WAS ANGRY AT
HIMSELF BECAUSE HE
ACCIDENTALLY LEFT THE
THE KEYS TO HIS CAR
AT HIS FRIEND'S HOUSE.

I am a type of food that is often found in the fridge and can be white in colour. What I am?
Hint 1: I am a dairy product.
Hint 2: You can spread me on the bread.

What has one letter and starts with an E?

I have a head like a cat and feet like a cat, but I am not a cat. What am I?

You may enter, but you may not come in. I have space, but no room. I have keys, but open no lock. What am I?

A new Engineering building containing 100 offices had just been completed. John was hired to paint the numbers 1 to 100 on the doors. How many times will John have to paint the number nine (9)?

I am soft and cuddly that soothe your heart. But, If you pick my last name I am going to tear you all apart. Who am I?

Why 1729 is a magic number? Answer Logically.