Page 58 - TG_G1_CH6_CHRIS

Think Addition to
Subtract Tens
Have children draw Carol’s lilies and roses in the picture.
• Carol has 20 lilies and 20 roses in her garden.
• Draw Carol’s flowers. Write an addition sentence and its related fact.
Ask: How many lilies does Carol have? 20
How many roses does Carol have? 20
Complete the addition sentence. 20 + 20 = 40
Complete the subtraction sentence. 40 – 20 = 20

ANCHOR ACTIVITY

Use the Anchor Activity for this lesson as a warm-up to gauge
children’s prior knowledge and help them engage at the
20 + 20 = 40 beginning of class.

40 − 20 = 20
1.NBT.6 Subtract multiples of 10 in the range 10–90 from multiples of 10 in the range 10–90 (positive or zero differences). Using concrete
models or drawings and strategies based on place value, properties of operations and/or the relationship between addition and
subtraction, relate the strategy to a written method and explain the reasoning used.
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TIME TO LEARN
TIME TO LEARN

1 20 + 30 = 50
50 Remind children how to use the fact-family triangle. The base of the
2 50 − 20 = 30 triangle usually shows the addends, while the top of the triangle usually shows
20 30 the sum.
3 50 − 30 = 20
Ensure that children know that if they have the number in the top of the
STEP triangle and one number from the bottom, they can perform subtractions to
BY
STEP Write the missing numbers.
find the other number in the bottom (base). Draw an empty triangle and write
1 70 + 10 = 80 80 numbers 20, 30, and 50 on the board.
80 − 70 = 10
80 − 10 = 70 70 10 Ask:
Where can you write the 20? bottom
2 40 + 50 = 90 90 Where can you write the 50? top
90 − 40 = 50 Where can you write the 30? bottom
40 50
90 − 50 = 40 Write three operation sentence? 20 + 30 = 50, 50 – 20 = 30, 50 – 30 = 20
3 40 + 20 = 60 60 30 + 20 = 50
60 − 20 = 40
20 40
60 − 40 = 20
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