--- title: "Comparing prices properly" description: "A lower shelf price does not always mean a lower cost per gram, item or use. Compare matching units, check offers and consider how much you will use." canonical: https://lightmysky.com/learn/life-skills/comparing-prices-properly-mt_v3i0WMP-Sl source: https://lightmysky.com/learn/life-skills/comparing-prices-properly-mt_v3i0WMP-Sl.md retrieved: 2026-11-12 --- > **Agent view.** This is the Markdown twin of the page, for tools and assistants. > When to use this site, and the call that answers each job: https://lightmysky.com/agent-instructions.md > API description (OpenAPI 3.1): https://lightmysky.com/openapi.json · Authentication: https://lightmysky.com/auth.md > Pricing: https://lightmysky.com/pricing.md · Catalog: https://lightmysky.com/llms.txt · Full catalog: https://lightmysky.com/llms-full.txt > Every machine-readable file on this domain: https://lightmysky.com/.well-known/ai-catalog.json > Ask for Markdown with `Accept: text/markdown`, a `.md` address, or `?mode=agent`. # Comparing prices properly A lower shelf price does not always mean a lower cost per gram, item or use. Compare matching units, check offers and consider how much you will use. Subject: Life Skills · Area: Money & Finance · Ages 12 to 13 Page: https://lightmysky.com/learn/life-skills/comparing-prices-properly-mt_v3i0WMP-Sl ## Ready when they can - Compare two products by unit price rather than by shelf price - Work out the cost per wear or per use for something bought once and used often - Spot one offer where buying more does not lower the unit price ## Lesson: Which pack is really cheaper Unit price is price divided by amount. Compare the same product in matching units. One kilogram is 1,000 grams. For a price per 100 g, divide the price by the number of 100 g portions: 600 g has six. You need both price and quantity. Use a calculator if needed, and keep extra decimal places until you compare. **Example.** Four identical pencils cost $3, while ten cost $8. Divide $3 by 4 to get $0.75 per pencil. Divide $8 by 10 to get $0.80 per pencil. The four-pack has the lower unit price. More pencils in a pack does not guarantee a lower price per pencil. Cost per use is price divided by uses. A $72 backpack used 24 times costs $3 per use. A $50 one used 10 times costs $5 per use. Future uses are estimates; fewer uses raise the cost per use. To find the uses needed for a target cost, divide price by that target: $72 divided by $3 gives 24 uses. A bulk offer can have a lower, equal or higher unit price. Compare equal amounts. If 1 litre of the same juice costs $3, four small bottles cost $12. A 4-litre bottle at $13 costs more for the same amount. If it cost $12, there would be no saving per litre. Use the final price and the full quantity in an offer. If a coupon applies, subtract its discount before dividing. Include free items in the quantity: buying four pens and getting one free gives five pens. Divide the price paid by five. Check the offer's conditions before using it. Compare products of similar quality and size. Rolls with different sheet counts are not equal amounts. Check whether the total price fits your budget and whether you will use the contents before they spoil. Online, read the stated quantity rather than judging from a photo. **Example.** In this example, four quarts make one gallon. A quart of milk costs $1.50, so four cost $6. A gallon of the same milk costs $5.20. The gallon is cheaper for the same amount. Comparing equal totals avoids rounding the price per quart. **Recap.** Compare matching amounts or uses. Include discounts and free items, then check the total price and how much you will use. *Price-comparison lesson, questions and flashcards written for this learning dataset. Source records were studied for teaching methods and question formats.* ## Practice 14 questions on this page, each with its working shown. ## Needs first - [Ratio Problems](https://lightmysky.com/learn/mathematics/ratio-problems-mt_h0gJcSuwdL) ## Optional connections - [Your first bank account and card](https://lightmysky.com/learn/life-skills/your-first-bank-account-and-card-mt_YoV2gRHaLS) ## Opens up - [Spending Inside Games and Apps](https://lightmysky.com/learn/life-skills/spending-inside-games-and-apps-mt_DCmLETXmjd) - [Saving for Something Months Away](https://lightmysky.com/learn/life-skills/saving-for-something-months-away-mt_NFZG8bDa5o)