Double Trouble

Show two rows of three beads on the Slavonic abacus. Ask the students to show you three and three on their fingers. Many of them will know that this is six fingers altogether. Ask them what they will need to do in order to change their fingers to four and three (add one finger). Ask them what 4 + 3 must be. Record the equation on the board or modelling book. Ask the students to show you how they changed 3 + 3 into 4 + 3 on the abacus.

Ask the students to look at the beads and see if they can help work out the answer without counting each bead. Look for answers based on 10 + 4 = 14. Note that this requires knowledge of the teen numbers. Ask the students what they would do to change 7 + 7 into 8 + 7 (add one), and what the answer would be.

Pose similar problems. For example: 6 + 6 = 12 so 7 + 6 = ?, 9 + 9 = 18 so 8 + 9 = ?, 8 + 8 = 16, so 7 + 8 = ?.

Repeat these doubles with fingers, tens frames, and Fly Flip cards. For example, two students act like mirrors facing each other and show seven fingers. They match the full hands (10) and the two twos (four). Similarly two Fly Flip cards showing seven can be put down. Two fives will be visible and two twos will be behind their backs.

Activity – Another Way of Doubling

Another representation is to place two of the same tens frame cards side by side. Talk about the fives structure and point to the two rows of five. “How many dots is that? How many dots altogether?” For example, 6 + 6 = 12.

Activity

The students could play Double Somersaults Plus or Minus One to consolidate their doubles and related facts.