* Mark up
Meaning - to raise the price on something
Example: The store marked up the price of the jacket I wanted.

* Mark down
Meaning - to lower the price of something
Example: There was a significant mark down on the sofa, so I bought it.

* Mark out
Meaning - to make boundaries around a certain area
Example: The construction workers marked out the area that they were demolishing.

* Mark off
Meaning - to cross off something that has been completed
Example: Each time I found an item in the store, I marked it off my list.

- "Back to square one"
meaning: to start all over again
Example: Well, that science experiment was a failure, back to square one to try to find another solution.

-"Whatever floats your boat"
meaning: whatever it is that makes you happy
Example: Charlie loves skiing, but I hate the snow. Oh well, whatever floats his boat is fine with me!

-"It's like finding a needle in a haystack"
meaning: it will be impossible to find
Example: I had to find my book in my brother's room but since it was so messy it was like finding a needle in a haystack.