These questions compare packages of identical or comparable goods, ask for a standardised price, or ask how much a better-value choice saves. A lower checkout price alone does not establish better value when the quantities differ.
Standardise every comparison
Choose one comparison direction and use it for every product. Price per item, price per litre or price per 100 grams is found by dividing price by the matching quantity. For example, 9 identical bars costing 6.30 dollars have a unit price of 0.70 dollars per bar. Lower price per unit means better value.
| Question form | Method |
|---|---|
| Price per item or per measurement unit | Divide each price by its quantity, using the same unit for every product. |
| Price per 100 grams | Convert each mass into groups of 100 grams, then divide its price by that group count. |
| Quantity per dollar | Divide quantity by price for every product; in this direction, the higher result gives better value. |
| Savings per unit | Find both unit prices first, identify the lower one, then subtract lower from higher. |
| Equal value at a new pack size | Multiply the original unit price by the new quantity. |
Keep the comparison like for like. Convert kilograms to grams or litres to the same volume unit before dividing. Money per quantity and quantity per money are both valid approaches, but mixing the two directions reverses the meaning. Comparisons also assume the goods have the same relevant quality.
Where mistakes happen
| Tempting route | How to reject it |
|---|---|
| Choose the package with the lower total price | A smaller package often costs less at checkout but more for each unit. Calculate matching unit prices before choosing. |
| Attach price-per-unit words to a quantity-per-money calculation | Price divided by quantity gives money per unit; quantity divided by price gives units per dollar. Keep the division and wording aligned. |
| Use the difference between total prices as the value comparison | Different package sizes make that difference misleading. Subtract only after both prices have been reduced to the same unit. |
| Call two differently sized products equal value because both seem close | Compute both rates to the requested precision. Small unit-price differences can be hidden by larger package totals. |
Try it
A 750 g bag of rice costs 3.00 dollars. Enter its cost per 100 g in dollars.
Bag A has 500 g of apples for 2.20 dollars, Bag B has 750 g for 3.15 dollars, and Bag C has 1 kg for 4.50 dollars. All apples are the same variety and quality. Which statements are true? Select all that apply.
- Bag B is the best buy.
- Bag A has a lower unit price than Bag C.
- Bag C has the highest unit price.
- Bag A has a lower total price than Bag B.
- Bag A is the best buy because its total price is lowest.
Nine identical sponges cost 7.20 dollars. At what price would a 12-sponge pack have exactly the same value per sponge?
- 8.00 dollars
- 10.20 dollars
- 9.60 dollars
- 12.00 dollars