Give the students calculators. Explain that they are to use the calculator to find pairs of numbers that have a sum of six, and then model each addend pair with their pasta. As they find the addend pairs, ask them to record them on the Addends and Sums Activity Sheet.
When they have finished, ask them to write addition and subtraction sentences for one of the rows of the chart. Remind them to use zero as one of the addends for each sum. Repeat with other numbers if you wish. At an appropriate time, ask the students to share the sentences they wrote.
Next, demonstrate how they can use an addition chart to find differences. Choose a number in the interior of the chart, and the number at the top of the column it appears in. The addends for the number that will be the number at the top of the same column and the number at the far left of the same row. You may wish to distribute the Addition Chart to students.
Call on volunteers to show how to find other differences.
Now put the students in pairs and display the Calculators and Hundred Boards:
Displaying Number Patterns tool. Assign two pairs at a time to take turns finding and recording differences using the online calculator.
Ask those pairs of students not at the computer to play a concentration game in pairs. Using their Addends and Sums Activity Sheets from earlier in the lesson, have them write one subtraction sentence without the answer on each of four index cards, and the answers on four other cards. Next, have one student in each pair collect and shuffle the 16 cards and place them upside down in a 4 × 4 array. The other student should go first in turning over two cards. If the differences match, he or she keeps the cards and takes another turn. If the differences do not match, the cards are returned to the array and the other student takes a turn. Tell the
students to continue playing until all the cards have been removed from the array. Then have the pairs of students exchange the card decks that they made and play the game again.
