Outdoor Subtraction Adventure!
Let's take math outside and learn how to subtract bigger numbers using columns!
Warm-up: Nature Count & Subtract (5 mins)
Quickly gather a small collection of similar items (e.g., 15 leaves, 12 pebbles). Ask: "If we have 15 leaves and 4 blow away, how many are left?" Practice a few simple subtractions orally.
Introduction: Chalkboard Math (10 mins)
On a paved area using chalk, write down a 2-digit subtraction problem vertically (e.g., 45 - 23). Explain the concept of columns: ones place and tens place. Model subtracting the ones column first, then the tens column. Use stones or sticks beside the numbers to represent the quantity in each place value.
Example:
Tens | Ones 4 | 5 (Represent with 4 big stones, 5 small pebbles)- 2 | 3 (Remove 2 big stones, 3 small pebbles)------- 2 | 2
Activity 1: Subtraction Stepping Stones (15 mins)
Draw several large subtraction problems on the pavement without borrowing. Have Karina use large stones (for tens) and small pebbles (for ones) to represent the top number. Then, physically remove the stones/pebbles representing the bottom number to find the answer. Write the answer with chalk.
Activity 2: The Borrowing Bridge (15 mins)
Introduce subtraction with borrowing (e.g., 52 - 17). Use chalk and stones/pebbles again. When needing to subtract the ones (2 - 7), explain we need more ones. Show how to 'borrow' or 'regroup' one ten (one big stone) and exchange it for ten ones (ten small pebbles). Place the ten pebbles in the ones column. Now subtract the ones (12 - 7), then the remaining tens (4 - 1). Repeat with a few more examples, letting Karina lead.
Activity 3: Measure & Subtract Dash (10 mins)
Use a measuring tape. Measure two distances (e.g., from a tree to a bush = 85 cm, from the tree to a flower = 38 cm). Ask Karina: "How much further is the bush than the flower?" Have her set up the subtraction problem (85 - 38) on the pavement with chalk and solve it, using borrowing if needed. Do a couple more measurements and subtractions.
Wrap-up & Check (5 mins)
Review one of the problems Karina solved. Ask her to explain the steps she took, especially the borrowing part. Discuss: "When might we need to subtract things outside?" (e.g., distances, counting collected items, time differences).
Differentiation: If Karina grasps the concept quickly, introduce 3-digit subtraction or problems with borrowing across multiple place values. If she needs more support, focus only on 2-digit subtraction without borrowing first, using plenty of physical manipulation with the stones/pebbles.