Worked solution
Biscuit discounts: undo the correct discount first
A shop selling biscuits gave the following offers. A customer who bought a total of 5 or more packets of biscuits was given a discount, regardless of the types of biscuits bought. A 10% discount was given if 5 to 8 packets were bought and a 20% discount if more than 8 packets were bought.
The following table shows the number of packets bought and the total amounts that three customers paid.
| Type of biscuits | Mrs Chan | Mr Lim | Mr Tan |
|---|---|---|---|
| Cream | 3 | 5 | 2 |
| Marie | 1 | 2 | 1 |
| Almond | 3 | 5 | 1 |
| Total amount paid in $ | 10.35 | 15.72 | 6.40 |
Calculate the price per packet for each type of biscuit before the discount. marks
[2013/RI/Promo/2]
CJC · Review Problems · Question 3
Answer
Cream $1.60; Marie $1.45; Almond $1.75 per packet.
Select each discount
The packet totals are 7, 12 and 4. Mrs Chan pays 90% of the undiscounted total, Mr Lim pays 80%, and Mr Tan receives no discount. Let undiscounted prices of Cream, Marie, Almond be dollars.
Set up the system
Thus , , .
Solve before-discount prices
The source GC solution is . Prices per packet before discount are $1.60 Cream, $1.45 Marie and $1.75 Almond. Applying the 90%, 80%, 100% payment factors recovers the table totals.
Common mistakes
Discount eligibility depends on the total packet count, not each biscuit type separately.
Solution notes
Also printed as Review 3 in both CJC Linear Equations lecture copies: question PDF page 13 / printed 173; answer PDF 15 / Student printed 175, Teacher visible footer 15 (extracted 175). Compared in evidence/review-cjc-linear-equations-lecture.md; the repeated asks, tables and marks retain this existing identity.