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# Teens and Fingers

Achievement Objectives:

Achievement Objective: NA1-1: Use a range of counting, grouping, and equal-sharing strategies with whole numbers and fractions.
AO elaboration and other teaching resources
Achievement Objective: NA1-3: Know groupings with five, within ten, and with ten.
AO elaboration and other teaching resources

Specific Learning Outcomes:

Solve subtraction problems from 20 by separating sets and counting all the objects.

Solve subtraction problems from 20 by counting all the objects in their head.

Recall the facts up to 10, and the teen facts.

Description of mathematics:

Number Framework Stage 2 to 4

Activity:

Check students know that teen means ten so they can decode a teen word as ones plus a ten. For example sixteen means six and ten. Check that in the two teen words that do not quite fit the pattern namely fifteen and thirteen that the students know “fif” means five and “thir” means three. The students need to know that the two unsystematic “teen” words twelve and eleven actually mean ten and two, and ten and one respectively.

Problem: Vincent has 14 snack packs and he eats one every day of the week for his lunch at school. How many packs does he have left at the end of the week?

Record 14 - 5 on the board. Put the students in pairs and get them to negotiate how to show 14 fingers between them. Normally one student shows 10 as 5 + 5 and the othershows 4. Removing 5 from 10 leaves 5. So the answer is 4 from one student and 5from the other which together is 9. Record 14 - 5 = 9 on the board.

Note that none of the problems below require going across a five. For example 12 - 4 is not asked because it would require the students to use part-whole thinking by removing 2 then 2 more out of the hands showing 10. This type of problem is delayed until the part- whole sections.

Examples. Word stories and recording for: 14 – 4, 8 + 5, 7 + 5, 20 – 5, 5 + 10, 17 –7, 12 - 5....

Challenging examples. Word stories and recording for 14 - ? = 9, 8 + ? = 13, 4 + ? = 14, 20 - ? = 10. ? + 4 = 14.