Counting Crocodiles

Introduction:

• Begin the lesson by reading “Counting Crocodiles”. As you read, encourage students to count along with you.
• After reading the book, ask students what kind of pattern the crocodiles made.
  • Students may need help recognizing that the crocodiles made a growing pattern on the way to the island and a shrinking pattern on the way back from the island.
• Organize the class into small groups of two or three students, giving each group 55 unifix cubes. Each group should have two colours of unifix cubes.

Lesson:

• Tell students that they are in charge of making their own crocodile bridge to cross the Silibobble Sea. Each unifix cube will represent one crocodile (e.g., link two cubes to represent two crocodiles).
• Students work together to compose all 10 of the crocodile combinations and organize them in 
• the correct order (least to greatest/1-10) to form the bridge across the Silibobble Sea. The bridge should look like this:
  • First Combination = One cube
  • Second Combination = Two cubes
  • Third Combination = Three cubes etc.
  • Tenth Combination = 10 cubes
• When students have used up all 55 cubes, have them double check that their bridge forms the same growing pattern that they saw in the story.
• Using a piece of paper and a pencil, have students label their 10^th crocodile combination with a number sentence representing how they composed 10 (e.g., if a student used six green unifix cubes and four orange unifix cubes, their number sentence will be 6+4 = 10). Place the piece of paper beside their 10^th crocodile combination.
• Have groups take turns presenting their 10^th crocodile combination and their number sentence to the class. Help the students conclude that there are many number combinations that can compose 10 (Appendix A).
• Have students arrange their crocodiles on the floor in numerical order (1-10) as if they were going to cross the Silibobble Sea.
• Give students time to cross the Silibobble Sea by stepping beside their crocodiles. Encourage them to count forwards and backwards as they cross the sea. Students can also practice skip counting by two as they cross every other crocodile combination.

Conclusion:

• Bring the class back together for a full-group discussion. Ask the students if it took more crocodiles to get to the island, or to return from the island?
  • Help students conclude that the same number of crocodiles were needed each way. When they build their 10 combinations, they will count up on the way there (1,2,3,4,5,6,7,8,9,10) and down on the way back (10,9,8,7,6,5,4,3,2,1) but the number of blocks used will be the same.
• Discuss how many ways there are to compose 10. After sharing their combinations, ask whether students can find any more combinations.
• Lastly, work together as a class to determine how many total monkeys crossed using the top of the crocodiles.