The purpose of this activity is to help students learn groupings within 20. For example 12 and 8 make 20; 16 and 4 make 20.
recall groupings within 20. For example 12 and 8 make 20; 16 and 4 make 20.
- Show the students how to make the calculator show pieces of 20. Do this by pressing the keys: “20 – 20 =”. Then, when any number less than 20 is entered, followed by the equals key, the calculator will display the remaining “piece” of twenty. For example, if “5 =” is entered, the calculator will display “15”. (Note that the result is displayed as a negative number, but this can be disregarded.)
- Enter the number “12” into the calculator and say:
We have put the number 12 into the calculator. When we press the “=” key it will show us the remaining piece of twenty. What will that be?
- Once students have given their answers, show them that the answer from the calculator is 8.
- Continue as a whole group in this way, or have students work in pairs with one student entering the numbers into the calculator and the other identifying the “missing piece” of 20.
This activity can be repeated in a similar way to help learn groupings within 10.