In Python, strings are immutable while lists are mutable. What is the difference?

Write an expression that uses exactly 3 arithmetic operators with integer literals and produces result as 99.

Add parentheses to the following expression to make the order of evaluation more clear.

y % 4 == 0 and y % 100 != 0 or y % 400 == 0

How does the // operator differ from the / operator? Give an example of where // would be needed.