Place value and Rounding and compersating

I am learning different strategies addition and subtractions problems.  I learnt rounding and compensating and P.V Partitioning. 

Place value was easy.  I perfer place value because you don't have to ask the question Too much or not enough in rounding and compensating. I got stuck on rounding and compensating because of the Too much or not enough it was really tricky to under stand. I enjoy this learning because I learnt something new.