2. Addition and Subtraction 13 70 + 50 = 70 80 90 100 110 120 + 10 70 + 50 = 120 50 + 70 = 120

3. Addition and Subtraction 13 120 - 50 = 70 80 90 100 110 120 - 10 - 10 -10 - 10 -10 120 - 50 = 70

4. Addition and Subtraction 13 1.Select 2 cards to make tens numbers to add. 2.Add the tens numbers by counting forwards by tens. 3.Record your count on a number line. 4.Select an Ace and another card to make a tens number in the 100s, and another card to make a tens number to subtract. 5.Subtract the tens numbers by counting backwards by tens. 6.Record your count on a number line. Reflection: How can we add and subtract tens numbers? Investigations: Problem Solving Lola collected 80 cans. Jill collected 90 cans. How many cans did Lola and Jill collect altogether? Problem Solving Altogether Lola and Jill collected 80 cans. Jill collected 30 cans. How many cans did Lola collect?

5. Addition and Subtraction 13

6. 1.Sit with a friend. 2.Add 2 tens numbers on a calculator. 3.Check your answer by counting forwards by 10s on a number line. 4.Explain your strategy to a friend. Reflection: How can we add tens numbers? Investigations:

7. Addition and Subtraction 13 Investigations: 1.Sit with a friend. 2.Subtract a tens number from another tens number on a calculator. 3.Check your answer by counting backwards by 10s on a number line. 4.Explain your strategy to a friend. Reflection: How can we subtract tens numbers?

8. Addition and Subtraction 13 Investigations: 1.Cut a hundred chart into rows, for example. 2.Join the rows together to make a long number line between 1 and 100, for example, 3.Is a hundred chart a number line? 4.Why is a hundred chart joined into 10 rows, instead of 1 long row? 5.Is it because rows are easier to carry around and manipulate than one long row. Reflection: What is a hundred chart?

9. Addition and Subtraction 13 Investigations: 1.Cut a hundred chart into parts like a jigsaw puzzle, for example, 2.Put the hundreds chart back together. 3.Swap charts with a friend. 4.Put your friend’s chart back to together. Reflection: What is a hundred chart?

10. Addition and Subtraction 13 Investigations: 1.Place 2 counters on 2 tens numbers on a hundred chart. 2.Count forwards by 10s to work how many tens you need to add to the lower tens number to make the higher tens number. 3.Count backwards by 10s to work how many tens you need to subtract from the higher tens number to make the lower tens number. Reflection: How can we add or subtract 10s on a hundred chart?

11. Addition and Subtraction 13 Investigations: 1.Record a tens number and some vertical arrows upwards or downwards, for example, 50  2.Show it to friend. 3.Have your friend start on the number, and count forwards or backwards by 10s to work out what number they will end on, for example, 50, 60, 70, 80, 90 4.Record on a number line. 5.Record as an addition or a subtraction number sentence, for example, 50 + 40 = 90 Reflection: How can we add or subtract 10s on a hundred chart?