I used this independent work while teaching to the common core standard 2.NBT.B.6: I can add up to 4 two-digit numbers using different strategies.
I used Learnzillion.com to teach the lesson whole group. (Leanzillion is an awesome website you should be familiar with if you're not already!) After watching the video that correlates with this idependent work, students began math workshop stations.
Link to LearnZillion: Scroll to Section 4, Lesson Set 1
** If you're looking for the unit bundle, check out this link! **