You can add like this: Choose blocks that represent one of the numbers Choose blocks that represent the other of the numbers Put the two sets of blocks together, making change as required to end with the maximum number of highest-order blocks. Example 18 + 23 = ? Find a stick of 10 and 8 unit blocks to represent 18. Find 2 sticks of 10 and 3 unit blocks to represent 23. Put them together. You have 3 sticks of 10 and 11 unit blocks. Trade in 10 of the unit blocks for 1 stick of 10. You now have 4 sticks of 10 and 1 unit block. The result is 41. 18 + 23 = 41