A unit price divides cost by quantity, putting different package sizes on one comparable number.
Step 1: Let's Learn
Read it, or press Listen and follow the words.
Bigger is not always cheaper
Large packages usually cost less per unit, but not always. Checking takes seconds.
Unless it spoils
A cheaper unit price on food you cannot finish is not a saving. Cost per unit used is what counts.
Discounts do not add
20% off then a further 10% off is not 30% off. It is 0.8 × 0.9 = 0.72, which is 28% off.
Percent off a bigger number
30% off a $200 item saves more than 50% off a $100 item. The base matters as much as the rate.
Zero percent offers
Interest-free financing often carries a fee, or charges all deferred interest if one payment is late. Read the condition before accepting.
Unit price makes sizes comparable
Divide price by quantity to get cost per unit. Different package sizes cannot be compared any other way, and the larger pack is not always cheaper per unit despite the general expectation.
Successive discounts multiply
30% off then a further 20% off is not 50% off. It is 0.7 × 0.8 = 0.56, so 44% off. Percentages applied one after another compound, and the presentation relies on that being unintuitive.
A discount is not a saving
Spending 70 on an item marked down from 100 spends 70; it does not save 30 unless the item was going to be bought anyway. Reference prices are chosen to make the reduction look larger.
Bulk buying has conditions
A lower unit price is only a saving if the quantity is used before it spoils and the storage exists. Waste converts a per-unit saving into a total loss, which the shelf label cannot tell you.
Step 2: Try It Yourself
Tap and try it out.
Small
Medium
Large
Small has the most. It has 8 more than Medium.
Step 3: Watch an Example
One step at a time.
Watch Sana Combine Two Discounts
A $200 jacket is 20% off, with a further 10% off at the register.
- Step 1
20% off leaves 80% of the price: 0.8 × 200 = $160.
Step 4: Your Turn
Practice makes it stick.
The Unit Price
Problem 1 of 2
$6 for 4 litres. Price per litre, in dollars?
dollars
The Double Discount
Problem 2 of 2
A $200 item at 20% off then 10% off. Final price in dollars?
dollars
Which Is Cheaper?
1 of 8
$9 for 3 kg. Price per kg in dollars?
2 of 8
$10 for 4 kg. Price per kg in dollars?
3 of 8
$100 item at 25% off. Final price in dollars?
4 of 8
$80 item at 10% then 10% off. Final price in dollars?
5 of 8
30% off $200. Saving in dollars?
6 of 8
50% off $100. Saving in dollars?
7 of 8
Put the steps for comparing two package sizes in order.
- 1Divide price by quantity for each.
- 2Compare the two unit prices.
- 3Check you will actually use the larger amount.
- 4Note the price and quantity of each package.
8 of 8
$12 for 5 litres. Price per litre, to two decimal places?
Step 5: Quick Check
Show what you know.
Question 1 of 2
$15 for 5 kg. Price per kg in dollars?
Question 2 of 2
Is 20% off then 10% off the same as 30% off?
What You Learned
- A unit price makes different package sizes comparable.
- Successive discounts multiply rather than add.
- A percentage saving depends on the base it applies to.