What famous saying does this rebus mean?

COME SERVED <---
COME SERVED
COME SERVED
COME SERVED
COME SERVED

If,

6 / 7 = 2
3 / 9 = 7
8 / 2 = 6

Then

4 / 5 = ?

You throw me out when you want to use me and you take me in when you don't want to use me.

Who Am I?

The host of a game show offers the guest a choice of three doors. Behind one is an expensive car, but behind the other two are goats.
After you have chosen one door, he reveals one of the other two doors behind which is a goat (he wouldn't reveal a car).

Now he gives you the chance to switch to the other unrevealed door or stay at your initial choice. You will then get what is behind that door.

You cannot hear the goats from behind the doors, or in any way know which door has the prize.

Should you stay, or switch, or doesn't it matter?

You bought me for dinner but never eat me. What am I?

If six children and two dogs were under an umbrella, how come none of them got wet?

Can you think of a smallest +ve number such that if we shuffle the digits of the number, the new number becomes double the original number?

I’m tall when I’m young, and I’m short when I’m old. What am I?

There is a square of a particular number which when doubled, becomes 7 more than its quarter.

Can you find the number?

A man has eighty-one cows ( numbered 1,2,3...81 as such). The beauty is that cow no. 1 gives 1ltr of milk, cow no. 2 gives 2ltrs of milk and so on. The man wants to equally distribute the cows among his nine sons so that each one of them gets the same quantity of milk.