2. =
= 122
= 122
Addition and Subtraction 15

3. 125 – 50 =
125 – 50 = 75
Addition and Subtraction 15

4. Select cards to make tens number and a two-digit number to add.
Investigation:
Select cards to make tens number and a two-digit number to add.
Add the tens numbers by counting forwards by tens off the decade.
Record your count on a number line.
Select cards to make a tens number to subtract from a number with tens and ones.
Subtract the tens numbers by counting backwards by tens off the decade.
Reflection: How can we add and subtract tens numbers?
Problem Solving
Lola collected 84 cans. Jill collected 90 cans.
How many cans did Lola and Jill collect altogether?
Problem Solving
Altogether Lola and Jill collected 117 cans.
Jill collected 30 cans.
How many cans did Lola collect?
Addition and Subtraction 15

5. Addition and Subtraction 15

6. Add a tens number and a two-digit number on a calculator.
Investigation:
Sit with a friend.
Add a tens number and a two-digit number on a calculator.
Check your answer by counting forwards by 10s off the decade on a number line.
Explain your strategy to a friend.
Reflection: How can we add tens numbers?
Addition and Subtraction 15

7. Explain your strategy to a friend.
Investigation:
Sit with a friend.
Subtract a tens number from a number with tens and ones on a calculator.
Check your answer by counting backwards by 10s off the decade on a number line.
Explain your strategy to a friend.
Reflection: How can we subtract tens numbers?
Addition and Subtraction 15

8. Cut a hundred chart into parts like a jigsaw puzzle, for example,
Investigation:
Cut a hundred chart into parts like a jigsaw puzzle, for example,
Put the hundreds chart back together.
Swap charts with a friend.
Put your friend’s chart back to together.
Reflection: What is a hundred chart?
Addition and Subtraction 15

9. Reflection: How can we add or subtract 10s on a hundred chart?
Investigation:
Place 2 counters on 2 numbers with the same number of ones, for example 42 and 72 on a hundred chart.
Count forwards by 10s to work how many tens you need to add to the lower number to make the higher number.
Count backwards by 10s to work how many tens you need to subtract from the higher number to make the lower number.
Reflection: How can we add or subtract 10s on a hundred chart?
Addition and Subtraction 15

10. Reflection: How can we add or subtract 10s on a hundred chart?
Investigation:
Record a tens number and some vertical arrows upwards or downwards, for example, 56 i i i i
Show it to friend.
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, 56, 66, 76, 86, 96
Record on a number line.
Record as an addition or a subtraction number sentence, for example, = 96
Reflection: How can we add or subtract 10s on a hundred chart?
Addition and Subtraction 15