Odd and even numbers and arrays (grade 2) · lesson

Odd and even

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💡 An even number makes pairs with none left over. An odd number has one left over.

8 socks make 4 pairs. 8 is even.

7 fish make 3 pairs and 1 left over. 7 is odd.

🧠 How to think about it

Look at the ones digit. Even numbers end in 0, 2, 4, 6, or 8. Odd ones end in 1, 3, 5, 7, or 9.

🏡 Try it at home

Match socks from the laundry. Is there one left over? Is the number odd or even?

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💡 Every even number is two equal numbers added together.

14 = 7 + 7. 16 = 8 + 8. Both are even.

17 can't be split into two equal groups. 17 is odd.

🧠 How to think about it

Try to split the number into two equal groups. If it works, it is even.

🏡 Try it at home

Split 12 crackers fairly between two people. Then try 13. What happens?

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💡 When things are in equal rows, add the same number once for each row.

3 rows of 4 apples. 4 + 4 + 4 = 12.

5 rows of 3 chairs. 3 + 3 + 3 + 3 + 3 = 15.

🧠 How to think about it

Count how many in one row. Count the rows. Write the row number once for every row, then add.

🏡 Try it at home

Look at an egg carton. How many rows? How many in each row? Add them up.

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💡 A rectangle can be split into rows and columns of same-size squares.

Rows go across. Columns go up and down.

A rectangle with 3 rows of 5 squares has 15 squares.

🧠 How to think about it

Don't add the number of rows and the size of a row. Add the row size once for each row.

🏡 Try it at home

Find tiles on a floor or squares on a waffle. Count the rows and the squares.