Cogito
Consumer Math · Chapter 5 · Lesson 3
Comparison Shopping
Unit price, discounts, and the offers that are not.
12 problems · about 20 minutes · TEKS M.M.5.C
What this lesson teaches
The student compares prices using unit rates and evaluates discounts and financing offers.
- A unit price makes different package sizes comparable.
- Successive discounts multiply rather than add.
- A percentage saving depends on the base it applies to.
Warm Up
Straightforward practice. Get the method working first.
5 problems$15 for 5 kg. Price per kg in dollars?
Answer 3
Why $3.
Is 20% off then 10% off the same as 30% off?
Answer No, it is 28% off, because the second applies to a smaller price.
Why Successive discounts multiply.
$9 for 3 kg. Price per kg in dollars?
Answer 3
Why 9 ÷ 3.
$10 for 4 kg. Price per kg in dollars?
Answer 2.5
Why 10 ÷ 4.
$100 item at 25% off. Final price in dollars?
Answer 75
Why 0.75 × 100.
Build It Up
The same ideas with more to keep track of.
3 problems$80 item at 10% then 10% off. Final price in dollars?
Answer 64.8
Why 0.9 × 0.9 × 80.
30% off $200. Saving in dollars?
Answer 60
Why 0.30 × 200.
50% off $100. Saving in dollars?
Answer 50
Why 0.50 × 100.
Stretch Yourself
Mixed problems. Work out what kind of question it is before you start.
4 problemsPut the steps for comparing two package sizes in order.
Answer 1. Note the price and quantity of each package. 2. Divide price by quantity for each. 3. Compare the two unit prices. 4. Check you will actually use the larger amount.
Why The waste check comes after the arithmetic.
$12 for 5 litres. Price per litre, to two decimal places?
Answer 2.4
Why 12 ÷ 5.
The Unit Price: $6 for 4 litres. Price per litre, in dollars?
Answer 1.5 dollars
Why $1.50.
The Double Discount: A $200 item at 20% off then 10% off. Final price in dollars?
Answer 144 dollars
Why $144.