Can you find the missing piece of the Porsche?

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

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.

I make two people out of one. What am I?

Twice ten are six of us,

Six are but three of us,

Nine are but four of us;

What can we possibly be?

Would you know more of us?

Twelve are but six of us,

Five are but four, do you see?

What are we?

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

Can you name three consecutive days without using the words Monday, Tuesday, Wednesday, Thursday, Friday, Saturday, or Sunday?

When my father was 31 I was 8. Now he is twice as old as me. How old am I?

I get hot but I never sweat,
I cook food but I am not a chef,
I have a door but you can't enter me,
I have a light but I am not a lamp.
Who am I?

Can you name any English verb that becomes its past tense by simply rearranging the alphabets ?