Shopping Spree Mass Challenge: Adding Grams and Kilograms

This engaging activity for Year 3 focuses on the practical application of adding masses, specifically grams (g) and kilograms (kg). Children will create a 'shopping list' of items with given masses, calculate the total mass of their shopping, and then compare their list with a partner's to determine whose shopping is 'heavier' or 'lighter'. This activity reinforces understanding of mass units and develops addition skills within a real-world context, aligning with the Year 3 National Curriculum objective for measurement: 'add and subtract amounts of money to give change, using both £ and p in practical contexts' (though adapted here for mass).

1. Introduction (5-10 minutes): Begin by reviewing units of mass: grams (g) and kilograms (kg). Show examples of items that might be measured in grams (e.g., a packet of crisps, a small apple) and kilograms (e.g., a bag of potatoes, a school bag). Discuss the relationship: 1 kg = 1000 g. Use a balance scale or kitchen scales to demonstrate the mass of a few common classroom objects.
2. Shopping List Creation (15-20 minutes): Distribute the 'Shopping Item Cards' to each child or pair. Explain that they need to choose 5-7 items for their 'shopping list'. They should record the item name and its mass on their 'Shopping List Worksheet'. Encourage them to think about a balanced shop (e.g., some lighter items, some heavier ones).
3. Calculating Total Mass (15-20 minutes): Guide children to add up the masses of the items on their individual shopping lists. Remind them to be careful when adding grams and kilograms. For example, if they have 500g and 750g, they should recognise this as 1250g, which is 1kg 250g. Provide whiteboards for working out if needed.
4. Partner Comparison (10-15 minutes): Once children have calculated their total mass, pair them up. They should compare their total mass with their partner's. Ask them to discuss: 'Whose shopping is heavier?' 'Whose is lighter?' 'What is the difference in mass between our two shopping lists?' (This introduces subtraction of mass, which can be a good extension).
5. Plenary (5-10 minutes): Bring the class back together. Ask a few pairs to share their shopping lists and total masses. Discuss strategies they used for adding. Address any common misconceptions about converting between g and kg or adding different units. Reinforce the importance of knowing units of mass in everyday life.

• Shopping Item Cards: Create cards with pictures and masses of various common shopping items (e.g., 'Loaf of Bread - 800g', 'Bag of Apples - 1kg 200g', 'Packet of Biscuits - 250g', 'Carton of Milk - 1kg', 'Small Bag of Rice - 500g', 'Tin of Beans - 420g', 'Large Watermelon - 3kg 500g', 'Box of Cereal - 375g'). Ensure a good mix of grams and kilograms.
• 'Shopping List Worksheet': A simple sheet with columns for 'Item Name', 'Mass (g/kg)', and a space at the bottom for 'Total Mass'.
• Whiteboards and pens: For working out calculations.
• Optional: Real-life objects and a balance scale/kitchen scales for the introduction.
• Optional: Number lines or base ten blocks for visual support with addition.

Children will be successful if they can:

• Accurately record the mass of chosen items.
• Correctly add at least 5 masses together.
• State the total mass of their shopping list, using appropriate units (g and kg).
• Compare their total mass with a partner and identify who has the heavier/lighter shopping.
• (Extension) Calculate the difference in mass between two shopping lists.