# Abacus Math Program – Lesson 15 – Forward Double Rod

Here we will explore the final bead movement in our basic skill training program that looks at executing the 10 pair addition rule twice across two adjacent rods, called the Forward Double Rod. We discussed in Lesson 13 and Lesson 14 the idea of repeatedly using the same basic bead movements over and over again to solve more complex problems. We can extend this idea across as many rods as necessary to complete the addition operation. For instructional purposes we will show this interaction across two adjacent rods.

If we consider the example 95 + 5, we know we must use the 10 pair addition rule. The first step in the addition rule is to add 1 to the next rod left. In this case, 9 is on the next rod so there are no available beads to add the 1. So to add 1 to 9 we must repeat the use of the 10 pair addition rule on the second rod. We are now incorporating the 10 pair addition rule twice across two rods which is the reason this movement is called the Forward Double Rod.

To complete the problem we need to add 1 to the rod left of the 9 and then subtract 9, the 10 pair of 1, from 9. Please note the 1 we are adding to the 9 is the 1 from the first use of the 10 pair addition rule. We complete the problem by subtracting 5, the 10 pair of 5, from 5 on the first rod. Using the 10 pair addition rule twice leaves us with 100 on the abacus.  