Seahorse and Starfish Math: Adding and Subtracting to 100!
Lesson Description
Video Resource
Starfish rulers | Addition and subtraction within 100 | Early Math | Khan Academy
Khan Academy
Key Concepts
- Addition and subtraction within 100
- Solving word problems
- Understanding 'more than' and 'fewer than'
Learning Objectives
- Students will be able to solve word problems involving addition and subtraction within 100.
- Students will be able to identify whether a problem requires addition or subtraction based on the keywords 'more than' and 'fewer than'.
- Students will be able to use place value to add two-digit numbers.
Educator Instructions
- Introduction (5 mins)
Begin by asking students if they've ever seen a starfish or seahorse. Introduce the idea of an underwater city ruled by starfish. Explain that today, they'll be math detectives, solving a mystery using addition and subtraction. - Video Viewing (7 mins)
Play the Khan Academy video "Starfish rulers | Addition and subtraction within 100 | Early Math | Khan Academy." Encourage students to pay attention to how the problem is set up and solved. - Discussion and Problem Solving (10 mins)
After the video, review the problem together. Ask students to explain in their own words what the problem is asking. Guide them through the steps of identifying the important information and deciding whether to add or subtract. Emphasize the meaning of 'fewer than' and 'more than'. - Practice Problems (13 mins)
Provide students with similar word problems to solve independently or in small groups. Encourage them to draw pictures or use manipulatives (like blocks or counters) to help them visualize the problems. Example problems: * There are 32 green fish and 15 blue fish. How many fish are there in all? * Sam has 64 shells. He gives 21 to his friend. How many shells does Sam have left? * There are 45 crabs which are 20 fewer than the number of turtles. How many turtles are there? - Wrap-up (5 mins)
Review the main concepts of the lesson. Have students share their strategies for solving word problems. Briefly introduce the concepts covered in the next video. Assign the practice exercise on KhanAcademy.org.
Interactive Exercises
- Seahorse and Starfish Count
Provide students with pictures of seahorses and starfish (or use counters). Give them different scenarios (e.g., 'There are 25 seahorses and 12 more starfish than seahorses. How many starfish are there?'). Have them use the pictures or counters to solve the problems. - Word Problem Creation
Have students work in pairs to create their own word problems involving seahorses and starfish. They should then exchange problems with another pair and solve them.
Discussion Questions
- What does 'fewer than' mean? How does it help us decide if we should add or subtract?
- What does 'more than' mean? How does it help us decide if we should add or subtract?
- Can you think of a time when you needed to add or subtract to solve a problem in your own life?
Skills Developed
- Problem-solving
- Addition and subtraction within 100
- Reading comprehension
- Critical thinking
Multiple Choice Questions
Question 1:
What does 'fewer than' mean?
Correct Answer: Less
Question 2:
If there are 20 seahorses and 10 *more* starfish, how many starfish are there?
Correct Answer: 30
Question 3:
Which number is bigger: 55 or 45?
Correct Answer: 55
Question 4:
What is 10 + 5?
Correct Answer: 15
Question 5:
What is 20 - 10?
Correct Answer: 10
Question 6:
If you have 3 cookies and get 2 more, how many do you have?
Correct Answer: 5
Question 7:
Which of these is an addition (+ ) problem?
Correct Answer: 2 + 2
Question 8:
Which of these is a subtraction (-) problem?
Correct Answer: 7 - 3
Question 9:
What is '10 more than' 20?
Correct Answer: 30
Question 10:
What does the word 'total' usually mean we should do?
Correct Answer: Add
Fill in the Blank Questions
Question 1:
Adding means we put numbers _________.
Correct Answer: together
Question 2:
Subtracting means we take numbers _________.
Correct Answer: away
Question 3:
The plus sign (+) means we should _________.
Correct Answer: add
Question 4:
The minus sign (-) means we should _________.
Correct Answer: subtract
Question 5:
10 more than 5 is _________.
Correct Answer: 15
Question 6:
5 fewer than 10 is _________.
Correct Answer: 5
Question 7:
When a number is 'less' than another number, it is _________.
Correct Answer: smaller
Question 8:
When a number is 'greater' than another number, it is _________.
Correct Answer: bigger
Question 9:
If there are 12 starfish and we add 3 more, there are _________ starfish.
Correct Answer: 15
Question 10:
If there are 15 seahorses and 5 swim away, there are _________ seahorses left.
Correct Answer: 10
Educational Standards
Teaching Materials
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