Basic Subtraction on the Cranmer Abacus Sara Larkin

Basic Subtraction on the Cranmer Abacus Sara Larkin Math Consultant Iowa Educational Services for the Blind and Visually Impaired

Prerequisites • The student should be able to count by rote • The student should be able to demonstrate the ability to count the number of objects in a group • The student should be able to demonstrate the concept of subtraction by taking a number of objects away from a group and telling you how many are left

Abacus Skills • The student must be able to set numbers on the abacus • The student must be able to read numbers on the abacus • The student must have a knowledge of the terms associated with subtraction on the abacus

Terms for Subtraction • Set: To “write” the first number of a subtraction problem on the abacus • Count: To move abacus beads, one at a time, away from the counting bar while counting numerically each time a bead is moved. • Return: To move either the four beads below the counting bar or the nine beads against the counting bar simultaneously toward the counting bar when a subtraction rule is applied.

Some Basic Problems • 9 – 3 • 14 – 2 • 35 – 20 • 99 – 23

Resource Millaway, S. M. (2002). Abacus basic competency: A counting method. American Printing House for the Blind.