Comparing best buys
Compare the value of products sold in different quantities or prices by working out and comparing unit prices (price per item or per unit of mass or volume), using a calculator where appropriate, and explain which is the better buy
Lesson
Set out your lesson
“Comparing best buys means practising the idea at the table with counters or paper models and one clear check. We will demo once, then your child tries.”
Bring to the table
- Small counters or grid paper
- Paper and pencil
Extra for the adult
Worked example. Three rows of four counters make 12. Write 3 × 4 = 12.
Optional challenge. For Comparing best buys, add one harder example after success.
What to notice. Keep one parent note: examples tried; results; support used. This session samples Comparing best buys, not mastery.
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Teaching approaches
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1 approach
Comparing best buys means practising the idea at the table with counters or paper models and one clear check. We will demo once, then your child tries.
Materials: Small counters or grid paper; Paper and pencil. Adult models 3 × 4 as three groups of four, then writes the product. Child builds three multiplication examples as equal groups and records each product. Done: three correct products with groups matching the writing. Stop after the fresh check; keep optional challenge for another day.
Family records and proof options
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Practice this concept
Start practiceComparing best buys practice
Practice key ideas from Comparing best buys.
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Learning resources
Extra practice links — they do not replace Gakuva’s teaching approach.
Illustrative Mathematics · Practice link — not the full lesson
Which detergent is a better buy?
Before you open · source notes
Detergent unit rates support comparing best buys. Not every interest calculation.
Free, no sign-in. A teacher solution is on the same page, so use the student view with your child.
Before you openAsk the learner which option is the better buy and explain using a unit rate.
Opening this link does not save learning or assess mastery.
Source, access and review notes
Public Illustrative Mathematics task page. The .html address responds HTTP 308 to this URL. An anonymous GET of this URL on 2026-11-12 returned HTTP 200 with no login or payment prompt. Where a teacher solution is present, it is on the same page as the student task; this check did not find a separate locked student view. An adult can use the student view section and should not read a solution aloud. Advertising was not observed in the fetched HTML text; that is not a browser, device, or ad-free guarantee. This is a paper or discussion task, not an automatically marked interactive game. Opening the link does not save practice or assess mastery. Diagrams on the page use missing or filename-only alt text, so they are not an accessible image equivalent. Accessibility still depends on an adult describing the picture.
Illustrative Mathematics. “Which detergent is a better buy?.” Licensed CC BY-NC-SA 4.0. External task; Gakuva does not copy, host, embed, or redistribute it.
CC BY-NC-SA 4.0 — link only
Check understanding
- Decide whether a 2 kg bag of rice for $5.80 or a 500 g bag for $1.60 is better value and explain why
- Work out the price per 100 g of two pack sizes of cereal and say which is cheaper per 100 g
- Explain why the bigger pack is not always the better buy (e.g. when the unit price is higher or the food would be wasted)
“At the supermarket, if there are two pack sizes of the same cereal, can your child work out which one is better value by comparing the price per 100 g?”
Curriculum record
- Type
- Procedural
- Subject
- Mathematics
- Domain
- Measurement
- Age range
- Ages 9–13
Standards