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.
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.
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.
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.
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.
Word Wall: hundreds, add, adding, addi-on, combina-ons to ten, doubles, bridge to ten, equa-on, turn arounds, solve, take away 2.2.4
7+10=17 7+20=27 7+30=37 7+40=47 7+50=57 7+60=67 7+70=77
20 + 17 = 37
10+23= 20+27 = 70+12=
48+10= 61+20= 27+30=
Subtrac3ng Friendly Numbers Con3nued 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.
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?
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.
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. 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 wheel, and numbers around the inner circle. Students apply the operation and write in the answers using washable pen. Digital Resources http://www.ideal-resources.com.au/index.php
83-10=73 83-20=63 83-30=53 83-40=43 83-50=33 83-60=23
48-10= 62-20= 27-20=
I have 70 Who has 10 less?
I have 50 Who has 20 more?
I have 55 Who has 5 less?
+20 20
22 14
9
16
80
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
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