Introduc3on Students will revise addi-on and subtrac-on strategies of coun-ng on, combina-ons to ten, doubles, near doubles, add ten and bridge through ten . Students will add the friendly numbers strategy to their range of strategies. Resources •  Early FISH Kit •  Hundreds board •  Transparent counters •  Mini-­‐ whiteboard and washable pens •  Bundle s-cks •  Calculator •  Addi-on and Subtrac-on strategy prac-ce cards •  Who has? More or less •  Number fact wheel •  Number line 1-­‐100 Time/Classroom Organisa3on Revise known strategies and apply to a range of addi-on and subtrac-on problems. Allow 20 minutes to introduce the near doubles strategy, and give students opportuni-es to prac-ce regularly. 2.2.4
Australian Curriculum Year Two ACMNA030 Solve simple addi-on and subtrac-on problems using a range of efficient mental and wri8en strategies Proficiency Strand:
Understanding – connecting number calculations with counting
sequences; combining numbers flexibly; identifying and
describing the relationship between addition and subtraction.
Reasoning – using known facts to derive strategies for
unfamiliar calculations
Ac3vity Process-­‐Adding Friendly Numbers 1.  Give each student a 1-­‐100 hundreds board. 2.  Ask them to place a counter on the number 7. 3.  Ask students to add 10 to 7 and place another counter on the answer. Write the equa-on on a whiteboard. 4.  Leave the counter on 7 and add 20. Write the equa-on on a whiteboard. Con-nue adding 30 through to 90 to 7. Write the equa-ons. Compare the equa-ons and discuss the pa8ern. Also discuss the turn-­‐arounds. 7+10=17
7+20=27
7+30=37
7+40=47
7+50=57
7+60=67
7+70=77
Word Wall: hundreds, add, adding, addi-on, combina-ons to ten, doubles, bridge to ten, equa-on, turn arounds, solve, take away
Adding Friendly Numbers Con3nued 1.  Clear off the hundreds board. Write the
equation: 17+20. Ask students to demonstrate
how they would solve this problem. Note that
when we added 2 tens to 17, the 7 did not
change.
2.  Check the answer using bundles sticks of tens
and ones.
20
+
17
=
37
3.  Give students a range of problems using
‘friendly numbers’. Encourage students to do a
mental calculation, and then check their answer
using the hundreds board or a calculator.
48+10=
61+20=
27+30=
10+23=
20+27 =
70+12=
Ac3vity Process Subtrac3ng Friendly Numbers 1.  Give each student a 1-100 hundreds board.
2.  Ask them to place a counter on the number 83.
3.  Ask students to take 10 away from 83 and place
another counter on the answer. Write the
equation on a whiteboard.
4.  Leave the counter on 83 and take away 20.
Write the equation on a whiteboard. Continue
taking away 30 through to 80. Write the
equations Compare the equations and discuss
the pattern.
Subtrac3ng Friendly Numbers Con3nued 83-10=73
83-20=63
83-30=53
83-40=43
83-50=33
83-60=23
1.  Clear off the hundreds board. Write the equation:
46-20. Ask students to demonstrate how they
would solve this problem. Note that when we
subtracted 2 tens from 46, the 6 did not change.
2.  Check the answer using bundles sticks of tens
and ones.
3.  Give students a range of subtraction problems
using ‘friendly numbers’. Encourage students to
do a mental calculation, and then check their
answer using the hundreds board or a calculator.
48-10=
62-20=
27-20=
Varia3ons & Extensions 1.  Number line addition
Resources: Number line 1-100
Repeat the above activity process. Use an unmarked
number line to add ‘friendly numbers’. Have students
draw a number line and place a number, for example:
38. Add 10 more. What number would you be on?
Add 20 more. Scaffold the discussion: do we need to
count in ones? Is there a quicker way to add each ten?
Resources: Who has? More or less
Give each student a card. The first student calls out the
question on the card. The student with the answer calls
out, and then continues with the next question. The game
continues until all the cards have been called.
I have 50
Who has 20 more?
I have 55
Who has 5 less?
I have 70
Who has 10 less?
3.  Number Wheel
Resources: Number fact wheel
Give each student a number fact wheel. Ask students to
write the addition or subtraction
operation you want to
practice in the centre of the
22 14
wheel, and numbers around
the inner circle. Students
80 +2 9
apply the operation and
200 16
write in the answers using
washable pen.
Digital Resources http://www.ideal-resources.com.au/index.php
Contexts for Learning Play:
Whole class addition to 25 game:
This game can be played as a small group game. Each
player takes 5 cards each.
Investigation:
Give students a number, for example 46. Give students 2
minutes and ask them to write as many questions as they
can which have that number as the answer.
Source: First Steps in Number – Understand Operations.
2010. Rigby: Port Melbourne. p136.
Real life experience:
Using junk mail, have students choose and circle three
prices to add and write the three amounts on their own
whiteboard. When finished share the strategies they have
used to add the amounts.
Routines and Transitions:
Use the whole class addition to 25 cards as a transition.
Have the Fact Wheels available for students to use when
they have finished other activities.
Assessment The number wheel activity could be used as an
assessment item to determine if students can add and
subtract ‘friendly numbers’.
Achievement Standard: perform simple addition and
subtraction calculations using a range of strategies.
Background Reading The development of any standard algorithms should
follow the development of mental and informal written
approaches and be introduced as an extension of
students’ existing strategies to enable them to deal with
larger numbers easily . It is now understood that
introducing standard written algorithms for simple
numbers can be counter-productive. For example, emphasising addi-on of two-­‐digit numbers in a standard column format where no trading is required actually encourages students to focus on each column separately and to lose sight of the significance of the places. This can lead to many of the errors they later make when trading is needed.
Source: First Steps in Number – Understand Opera-ons. 2010. Rigby: Port Melbourne. p144. Year three NAPLAN Numeracy test links Addi-on and Subtrac-on – number problems Addi-on and Subtrac-on – word problems Links to Related MAGs 2.1.4 – Func-on Machine 2.1.5 – Addi-on and Subtrac-on 1 2.3.2 – Number sequences 3.1.5 – Addi-on Strategies – 1 Suppor3ng Mathema3cal Vocabulary Development Providing a range of quality mathema-cal texts and text types that link to and extend the pupils’ interests. Crea-ng interac-ve working walls/displays so that pupils can capture vocabulary for later use. Adapted for use in the Cairns Diocese with the permission of the
Catholic Education Office Toowoomba