How to solve addition and subtraction customary weight word problems (Grade 3)

📚 Understanding Customary Weight

Customary weight refers to the system of weights commonly used in the United States. The primary units are ounces (oz) and pounds (lb). Knowing the relationship between these units is crucial for solving word problems.

• ⚖️ Ounce (oz): A smaller unit of weight.
• 💪 Pound (lb): A larger unit of weight. 1 pound is equal to 16 ounces.
• 🔄 Conversion: To convert pounds to ounces, multiply the number of pounds by 16. To convert ounces to pounds, divide the number of ounces by 16.

📜 A Brief History

The customary system has roots in old English measurement systems. These units have been refined over centuries and are still widely used today, especially in everyday contexts.

📌 Key Principles for Solving Word Problems

• ✔️ Read Carefully: Understand what the problem is asking. Identify the key information, including the weights given and what you need to find.
• ➕ Addition: Use addition when combining weights. For example, if you have two bags of flour and want to know the total weight.
• ➖ Subtraction: Use subtraction when finding the difference between weights or when taking away a certain amount.
• 🧮 Units: Always pay attention to the units. If the problem involves both pounds and ounces, you may need to convert to a single unit before solving.
• ✏️ Show Your Work: Write down each step to avoid mistakes and make it easier to check your answer.

💡 Real-world Examples

Example 1: Combining Weights

Sarah has a bag of apples that weighs 3 pounds and a bag of oranges that weighs 2 pounds. What is the total weight of the fruits?

Solution:

Total weight = Weight of apples + Weight of oranges

Total weight = 3 pounds + 2 pounds = 5 pounds

Example 2: Finding the Difference

A box of cereal weighs 18 ounces. John eats 5 ounces of cereal. How much cereal is left in the box?

Solution:

Remaining cereal = Initial weight - Weight eaten

Remaining cereal = 18 ounces - 5 ounces = 13 ounces

Example 3: Conversion and Addition

A package weighs 2 pounds and 4 ounces. How many ounces does the package weigh?

Solution:

• 1️⃣ Convert pounds to ounces: 2 pounds * 16 ounces/pound = 32 ounces
• 2️⃣ Add the remaining ounces: 32 ounces + 4 ounces = 36 ounces

The package weighs 36 ounces.

Example 4: Subtraction with Conversion

A bag of sugar weighs 5 pounds. You use 2 pounds and 8 ounces for a recipe. How much sugar is left?

Solution:

• 1️⃣ Convert 5 pounds to ounces: 5 pounds * 16 ounces/pound = 80 ounces
• 2️⃣ Convert 2 pounds and 8 ounces to ounces: (2 pounds * 16 ounces/pound) + 8 ounces = 32 ounces + 8 ounces = 40 ounces
• 3️⃣ Subtract: 80 ounces - 40 ounces = 40 ounces
• 4️⃣ Convert back to pounds and ounces: 40 ounces = 2 pounds and 8 ounces (since 40 / 16 = 2 with a remainder of 8)

There are 2 pounds and 8 ounces of sugar left.

✍️ Practice Quiz

Solve the following word problems:

1. 📦 A package contains two items. One weighs 1 pound and 5 ounces, and the other weighs 2 pounds and 3 ounces. What is the total weight of the package?
2. 🍎 A basket of apples weighs 4 pounds. If you remove 1 pound and 10 ounces of apples, how much does the basket weigh now?
3. 🍪 A baker uses 3 pounds of flour for cookies and 2 pounds and 6 ounces for a cake. How much flour did the baker use in total?
4. 🍫 A chocolate bar weighs 8 ounces. If you eat 3 ounces, how much chocolate is left?
5. 🎁 A gift box weighs 3 pounds and 12 ounces. What is its weight in ounces?

✅ Solutions

1. 3 pounds and 8 ounces
2. 2 pounds and 6 ounces
3. 5 pounds and 6 ounces
4. 5 ounces
5. 60 ounces

🔑 Conclusion

Mastering addition and subtraction of customary weights involves understanding the relationship between pounds and ounces and applying basic arithmetic operations. By practicing with real-world examples and paying close attention to units, you can confidently solve any weight-related word problem. Keep practicing, and you'll become a pro in no time! 🎉