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In this lesson and the next, we will use the grid to visualize the methods used to do arithmetic with two-digit numbers. For today, we’ll be looking at addition.
The first addition problem in this table is illustrated on the grid to the left. How many green squares are there? Click the first Rearrange button to move the squares around without changing how many there are, making it easier to count them. Enter your answer, and then click the Next button to continue to the second row.
Solve these addition problems in the standard way (by adding one column at a time), without using the grid.
Again, how many green squares are there? Use the Rearrange button in each row.
Now solve these addition problems in the standard way, without using the grid.
Notice that, in the two last sets of questions, you were doing exactly the same thing both times you solved each addition problem! That is, adding in columns is just like using the Rearrange button on the grid.