FURTHER EXPLORATION USING BEAD BARS
a. Sums with Parentheses
Aim: to give the concept of the associative property of addition
…colored bead bars
…box of signs for operations
The teacher presents the new symbols: ( ) parentheses. First a combination of three numbers is set up and the sum is completed. These signs are called parentheses; they group things. The same addition is repeated, now with the first two addends in parentheses. Whenever you see these parentheses in arithmetic, it means you must perform the addition inside the parentheses first. The first combination inside the parentheses is added, and the bead bar for the sum is placed below. The signs and bead bar for the next addend (outside the parentheses) are placed below as well. We find that this sum is the same as the original answer.
We haven’t changed the addends, and the sum hasn’t changed, only the addends have been grouped in a special way.
The teacher writes a long addition problem on a slip of paper. The child sets up the problem with the bead bars and signs, and computes the answer. The parentheses are placed around pairs of numbers. Review: We must perform the addition inside the parentheses first. New bead bars are put out for the sums of the pairs. These are added and the sum is found to be the same as the original problem
Note: Command cards may be made up for this work.