3
Repeated addition in arrays
Discover Mathematics P2: Term 2, Lessons 111–120
GoalUse repeated addition to find the total of an array of rows, and write two addition sentences.
New words
array · objects arranged in equal rows and columnsrow · objects going acrosscolumn · objects going up and downrepeated addition · adding the same number again and again
Explanation
An array puts objects in equal rows. This array has 3 rows with 4 apples in each row. Add the number in one row again for each row: 4 + 4 + 4 = 12. We can also look at columns. There are 4 columns with 3 apples in each: 3 + 3 + 3 + 3 = 12. The total is the same, so one array gives two addition sentences. To play rolling for rows, roll a die for the number of rows and a die for the number in each row.
Worked examples
2 rows with 5 oranges in each row. Add the rows: 5 + 5 = 10 oranges.
4 rows with 2 stars in each row. Add the rows: 2 + 2 + 2 + 2 = 8 stars.
Seif rolls a 3 and a 4. He makes 3 rows with 4 in each row: 4 + 4 + 4 = 12 counters.
Class activity
Rolling for rows. Roll a die twice. The first number is the rows and the second is how many in each row. Build the array with beans or buttons. Write the addition sentence for the rows. Then turn the paper and write the sentence for the columns. Do four rolls.
Practice
1
Write the addition sentence for the rows.
3 + 3 = 6.
2
5 rows with 2 books in each row. Write the addition sentence and the total.
2 + 2 + 2 + 2 + 2 = 10 books.
3
Write two addition sentences for the array.
Rows: 5 + 5 + 5 = 15. Columns: 3 + 3 + 3 + 3 + 3 = 15.
4
Marina rolls 2 and 5 and makes 2 rows with 5 stickers in each. How many stickers?
5 + 5 = 10 stickers.
5
A school has 3 rows of 3 chairs. How many chairs?
3 + 3 + 3 = 9 chairs.