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1 Ronald and his dad picked 80 apples.
They gave some apples to Ronald’s Problem-Solving questions 1 and 2 include:
grandma to make apple pies and took
the rest home. Ronald and his dad • Thinking addition to subtract tens
have 50 apples left. How many apples • Solving word problems concerning subtracting tens using the relationship
did they give to grandma? between addition and subtraction
30 + 10 = 80 - 50 = 30 apples
90 − 60 = 2 Mark had a box of 50 red and blue marbles. 20 of the marbles were In order to reinforce children’s ability to subtract tens using addition facts in
red. How many marbles were blue?
70 − 20 = real life situation, have them solve problem 1. Encourage them to read the
1. Write the subtraction sentence 2. Can you write another problem situation carefully and guide them to think addition in order to subtract tens to
and its related addition fact. for the same subtraction and
addition fact? find number of apples they gave to grandma. As 80 = 50 + 30, and then the
50 - 20 = 30 Answers will vary. Sample answer: Alice is working a puzzle with 50 pieces.
20 + 30 = 50 She has already placed 20 of the pieces. How many pieces are left? number of apples is 30 apples.
Then have children explore a situation that includes making inference and
Vocabulary Check Match.
justifying the answer using their own words in problem 2. Encourage them to
add tens 40 + 10 = 50, 50 – 40 = 10 think addition to subtract to find the number of blue marbles. As (5 = 3 + 2)
and(50=30+20). Then guide them to make their own clue and discuss it with them.
subtract tens 70 – 30 = 40
For more practice, copy the additional problems below onto the board for
think addition to 20 + 60 = 80
subtract tens group or individual work. The additional problems are based on subtracting
tens. In problems 1 and 2, ask: What addition fact helps you to solve the
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problem? How can you subtract tens using addition facts? Encourage them to
use the addition facts they learned to solve subtraction problems.
Vocabulary Check If children have difficulty, give them counters and help them make different
addition facts using counters to solve subtraction problems.
If children cannot complete the matches,
review Practice exercise A. Additional problem 1
Janine had 70¢; she bought some balloons for 30¢. How many cents does she
have left?
We can recall the addition fact of 30+40=70 , then 70 – 30 = 40 cents, she is left
with her 40¢.
EXIT ACTIVITY
Additional problem 2
There are 50 passengers on a bus. If 30 get off, how many passengers
Use the Exit Activity for this lesson to are left on the bus?
reinforce children’s understanding. This We can recall the addition fact of 20 + 30 = 50. Then 50 – 30 = 20. There are 20
can be used as an informal formative passengers on the bus.
assessment.

CLOSURE

Make sure children do not have any misconceptions. Ask:
What addition fact is used to subtract 60 – 20? 60

Children should recall the addition fact of 4 + 2 = 6 and 40 + 20 = 60 to subtract.
The opposite model shows the addition fact of 60.
The answer is 40.

20 40

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