For the work shown in the photos below, my son was solving the problem 42 + 26. This problem was one that I purchased in a set from Montessori for Everyone. First, he had to find the correct decimal cards to represent 42, then show the numeral with the beads. You can see he's done that in the photo below and is getting the beads he needs for 26.
We used a ruler for the "equals" sign. I showed him to put the units together first, count them, and find the large decimal card for the total (8 in this case), then he put the tens together, counted them, and found the correct decimal card (60 in this case). When the cards are stacked, they show the correct answer, 68.
Finally, I had him write the equation on this paper that I downloaded and printed from Montessori Print Shop (for free!)
This work was fairly easy for him, so our next lesson will be on "dynamic" addition equations which will require regrouping. We'll start with 2-digit, then move to 3 and 4-digit.