Understanding mass and weight is an important part of Year 3 mathematics. Learning how to add and subtract mass helps children develop problem-solving skills and prepares them for real-life situations.
This topic will explain how to measure mass, add and subtract mass, and solve mass-related problems in an easy-to-understand way.
What is Mass?
Mass is the amount of matter in an object. It is usually measured in grams (g) and kilograms (kg).
- Grams (g) are used for small objects, like an apple or a pencil.
- Kilograms (kg) are used for heavier objects, like a watermelon or a backpack.
💡 Tip: 1 kg = 1,000 g
How to Add Mass
Step 1: Identify the Units
Before adding, check if the mass is in grams or kilograms. If one number is in kg and the other in g, convert them into the same unit.
Example:
- A watermelon weighs 3 kg.
- A bag of sugar weighs 500 g.
Convert 3 kg into grams:
3 kg = 3,000 g
Now, add the masses together:
3,000 g + 500 g = 3,500 g
Convert back to kg if needed:
3,500 g = 3.5 kg
Example Problems for Adding Mass
-
A puppy weighs 4 kg. A kitten weighs 2 kg. What is their total weight?
- 4 kg + 2 kg = 6 kg
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A book weighs 600 g. A notebook weighs 400 g. What is their combined weight?
- 600 g + 400 g = 1,000 g (1 kg)
How to Subtract Mass
Step 1: Convert if Necessary
Just like addition, make sure both values are in the same unit before subtracting.
Example:
- A watermelon weighs 5 kg.
- A child eats 750 g of the watermelon.
Convert 5 kg into grams:
5 kg = 5,000 g
Now, subtract:
5,000 g – 750 g = 4,250 g
Convert back to kg if needed:
4,250 g = 4.25 kg
Example Problems for Subtracting Mass
-
A bag of flour weighs 3 kg. You use 1.5 kg for baking. How much flour is left?
- 3 kg – 1.5 kg = 1.5 kg
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A watermelon weighs 4,200 g. You eat 1,200 g. What is the remaining mass?
- 4,200 g – 1,200 g = 3,000 g (3 kg)
Word Problems Involving Mass
Example 1: Buying Fruits
Emma buys 2 kg of apples and 3.5 kg of bananas. What is the total weight of the fruits?
Solution:
2 kg + 3.5 kg = 5.5 kg
Example 2: Cooking Ingredients
A chef has 7 kg of flour. He uses 2.75 kg to bake a cake. How much flour is left?
Solution:
7 kg – 2.75 kg = 4.25 kg
Example 3: School Bag Weight
Liam’s school bag weighs 2.3 kg. He removes a book weighing 1.1 kg. What is the new weight of his bag?
Solution:
2.3 kg – 1.1 kg = 1.2 kg
Practice Exercises for Year 3
Try solving these problems on your own:
- A watermelon weighs 6 kg. A melon weighs 2 kg. What is their total weight?
- A pencil case weighs 350 g. A lunchbox weighs 1.2 kg. What is their combined weight?
- A dog weighs 8 kg. A cat weighs 4.5 kg. What is their total weight?
- A bag of rice weighs 5 kg. You use 3.25 kg. How much is left?
- A box of chocolates weighs 900 g. You eat 300 g. What is the remaining mass?
Adding and subtracting mass is an important math skill. By practicing with real-life examples, children in Year 3 can develop a better understanding of grams and kilograms.
Keep practicing, and soon, solving mass problems will become easy! 🚀