What does the idiom 'Grasping at straws' mean?

When you are desperate and you pursue every possibility no matter how unlikely

To win the lottery, or have something very fortunate happen

To be asked to do something that you don't want to do 

What does the idiom 'The tip of the iceberg' mean?

The problem is not as large as it appears to be 

Only a small part of the problem; the biggest part of the problem is hidden

A situation that quickly turns from bad to good

What does the idiom 'in dire straits' mean?

What does the idiom 'Dodged a bullet' mean?

to take advantage of a sale at the store 

A situation that is impossible to solve due to contradictory or illogical rules

Something used as the final chance when there are no other options available

A terrible place you would never want to visit