Removing element from list Python

See more:

Python

list1 = [5, 20, 15, 20, 25, 50, 20]

as you can see the list has been declared, now what I've must do is
1. remove all the elements valued at 20 and save them in the variable list2. After that print the variable list2.
2. from variable list 2. if has been found element valued at 15, changed to 10 and saved in the variable list3. also, print the list3
Sincerely, thanks before guys

What I have tried:

I have tried using function pops but it seems I just lost