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Lesson 7 ~25 min Unit 1 · Financial Maths +85 XP

Discounts and Sale Prices

Master shop sales — find sale prices, work out savings, and reverse-engineer the original from a sale tag.

Today's hook: A $\$180$ jacket is on sale for $\$126$. What percentage was taken off?
0/5QUESTS
Think First
warm-up

A $\$180$ jacket is on sale for $\$126$. What percentage was taken off? Jot down your first reaction — then we'll see who's right.

Record your answer in your workbook.
1
The Big Idea
+5 XP

Sales involve THREE quantities: marked (original) price, sale price, and discount. Knowing any two lets you find the third — both forwards and backwards.

A $\$180$ jacket is on sale for $\$126$. The discount in dollars is $180 - 126 = \$54$. The discount as a percentage is $\tfrac{54}{180} \times 100 = 30\%$. So this is "$30\%$ off". You can also reverse: knowing the sale price and the % off, find the original.

Discount $\%$ $= \dfrac{\text{Marked} - \text{Sale}}{\text{Marked}} \times 100$
Three numbers, three links
Marked, Sale, Discount — each pair finds the third.
Discount $\%$
Saving as a fraction of the ORIGINAL price.
Reverse for original
If sale = $70\%$ of marked, marked = sale $\div 0.70$.
2
What You'll Master
objectives

Know

  • Marked price = original (RRP)
  • Sale price = marked − discount
  • Discount can be % or dollars
  • Working backwards: marked = sale $\div$ (multiplier)

Understand

  • Why discount % is always on the ORIGINAL (marked) price
  • How to reverse to find the marked price from a sale price
  • The difference between sale price and discount

Can Do

  • Find sale price given % off
  • Find % off given marked and sale prices
  • Find marked price given sale price and discount %
3
Words You Need
vocabulary
Marked priceThe original price before any discount (RRP).
Sale priceThe price actually paid after a discount.
DiscountThe amount taken off the marked price.
SavingSame as discount — what you save in dollars.
Recommended Retail PriceManufacturer's suggested price — often the marked price.
Reverse percentageWorking back from sale price to find the original.
4
Spot the Trap
heads-up

Wrong: "Sale $\$126$, was $\$180$, so $\$126 \div \$180 = 70\%$ off" — NO. $70\%$ is what you PAY, $30\%$ is OFF.

Right: You pay $70\%$ ($\$126$); discount is $30\%$ ($\$54$). Sum to $100\%$.

Wrong: "A jacket's sale is $\$60$ at $25\%$ off. So the marked price was $60 + 25 = \$85$." — NO; the $25\%$ is not $\$25$.

Right: Sale $= 75\%$ of marked, so marked $= 60 \div 0.75 = \$80$.

5
Sale Price When You Know % Off
+5 XP

Forward problem — most common in shops. Given marked price and discount rate, find the sale price.

A $\$220$ guitar with $35\%$ off. Multiplier method: $\times (1 - 0.35) = \times 0.65$. $220 \times 0.65 = \$143$ sale price. The discount itself: $220 \times 0.35 = \$77$ saved. Check: $\$143 + \$77 = \$220$ ✓.

Sale $= $ Marked $\times (1 - $ Discount Rate$)$
Always pay $(1 - r)$
$35\%$ off = pay $65\%$.
Single multiplier step
Faster than subtraction.
Sale + savings = marked
Useful sanity check.
6
Reverse Discount Problems
+5 XP

Given the sale price and discount rate, find the original (marked) price. Reverse the multiplier.

A jacket on sale for $\$84$, after $25\%$ off. The $\$84$ is $75\%$ of the marked price. So marked $= 84 \div 0.75 = \$112$. Saving: $\$112 - \$84 = \$28$. Always DIVIDE by the pay-fraction, never multiply.

Marked $= \dfrac{\text{Sale}}{1 - \text{Discount Rate}}$
Divide, don't multiply
Reverse problems use $\div$.
By pay-fraction
$25\%$ off $\Rightarrow$ divide by $0.75$.
Sale > marked impossible
Multiplied by $<1$, sale must be less than marked.
Watch Me Solve It · The $\$180$ jacket
+15 XP per step
Q1
PROBLEM
A $\$180$ jacket is on sale for $\$126$. What percentage was taken off?
  1. 1
    Find discount in dollars
    $180 - 126 = \$54$
    Marked minus sale.
  2. 2
    Discount as % of marked
    $\tfrac{54}{180} \times 100$
    Discount/marked × 100.
  3. 3
    Compute
    $0.30 \times 100 = 30\%$
    So $30\%$ off.
Answer$30\%$ off
Watch Me Solve It · Sale price calc
+15 XP per step
Q2
PROBLEM
A $\$320$ watch has $40\%$ off. What is the sale price?
  1. 1
    Multiplier
    $1 - 0.40 = 0.60$
    You pay $60\%$.
  2. 2
    Multiply
    $320 \times 0.60$
    Sale price.
  3. 3
    Compute
    $320 \times 0.60 = \$192$
    Or: discount $= 0.40 \times 320 = 128$; $320-128=192$.
Answer$\$192$
Watch Me Solve It · Reverse the discount
+15 XP per step
Q3
PROBLEM
A scarf is on sale for $\$42$ after a $30\%$ discount. What was the marked price?
  1. 1
    Sale = $70\%$ of marked
    $42 = 0.70 \times M$
    Pay-fraction is $1 - 0.30 = 0.70$.
  2. 2
    Divide
    $M = 42 \div 0.70$
    Reverse: divide by pay-fraction.
  3. 3
    Compute
    $M = \$60$
    Marked was $\$60$; you save $\$18$.
AnswerMarked $= \$60$
8
Common Pitfalls
heads-up
Confusing pay $\%$ with off $\%$
Saying $70\%$ off when you actually pay $70\%$.
Fix: Off $+$ Pay $= 100\%$. Always check which is which.
Forward formula in reverse
Using $\times 0.75$ when going backwards — gives wrong answer.
Fix: Going BACKWARDS means DIVIDE. Sale $\div$ pay-fraction = marked.
Adding the discount % as dollars
Treating $25\%$ off as $\$25$ instead of $25\%$ of price.
Fix: Discount is a fraction OF the marked price.
Copy Into Your Books

Forward (Sale Price)

  • Sale $= $ Marked $\times (1 - r)$
  • $\$200$ at $25\%$ off $= \$150$
  • Discount $= $ Marked $\times r$

Reverse (Marked Price)

  • Marked $= $ Sale $\div (1 - r)$
  • $\$150$ at $25\%$ off $\Rightarrow$ marked $= \$200$
  • Divide, not multiply

Find % Off

  • $\%$ off $= \tfrac{M - S}{M} \times 100$
  • $\$80 \to \$60$ is $25\%$ off
  • Always on the marked price

Quick Sanity Check

  • Sale $+$ Saving $= $ Marked
  • Pay $\%$ $+$ Off $\%$ $= 100\%$
  • Sale $<$ Marked always

How are you completing this lesson?

D
Brain Trainer · Discounts and Sale Prices
4 problems

Four drill problems to sharpen your skills. Work each, then reveal the answer.

  1. 1 A $\$150$ shirt has $20\%$ off. Sale price?

    $150 \times 0.80 = \$120$.$\$120$
  2. 2 Sale $\$36$, marked $\$60$. What % off?

    $\tfrac{24}{60} \times 100 = 40\%$.$40\%$ off
  3. 3 Sale $\$108$ after $10\%$ off. Marked?

    $108 \div 0.90 = \$120$.$\$120$
  4. 4 A $\$45$ book is on sale for $\$36$. % off?

    $\tfrac{9}{45} \times 100 = 20\%$.$20\%$ off
Complete in your workbook.
1
A $\$160$ pair of jeans has $25\%$ off. Sale price?
+10 XP
2
A $\$50$ book is now $\$40$. What % off?
+10 XP
3
A sale price of $\$144$ reflects $20\%$ off. The marked price was:
+10 XP
4
Saving $\$45$ on a $\$150$ item is what % discount?
+10 XP
5
Sale price of $\$76.50$ after $15\%$ off — what was marked?
+10 XP
Show Your Working
9 marks total
Apply Medium 3 MARKS

Q6. Calculate the sale price for: (a) $\$240$ marked, $35\%$ off; (b) $\$1450$ marked, $12\%$ off; (c) $\$76$ marked, $42\%$ off.

Answer in your workbook.
Understand Easy 2 MARKS

Q7. Tahlia paid $\$32$ for a top that was on sale for $20\%$ off. (a) What was the marked price? (b) How much did she save?

Answer in your workbook.
Reason Hard 4 MARKS

Q8. A guitar normally costs $\$480$. During a sale it is reduced by $25\%$. After the sale, the shop adds a further markup of $20\%$ on the sale price. (a) Find the post-sale price. (b) Is the new price equal to the original $\$480$? Show working. (c) Explain why a $25\%$ discount followed by a $20\%$ markup is NOT the same as ending up where you started.

Answer in your workbook.
Comprehensive Answers

Quick Check

1. B — $\$120$.

2. B — $20\%$.

3. C — $\$180$.

4. B — $30\%$.

5. C — $\$90$.

Show Your Working Model Answers

Q6 (3 marks): (a) $240 \times 0.65 = \$156$ [1]. (b) $1450 \times 0.88 = \$1276$ [1]. (c) $76 \times 0.58 = \$44.08$ [1].

Q7 (2 marks): (a) Marked $= 32 \div 0.80 = \$40$ [1]. (b) Saved $= 40 - 32 = \$8$ [1].

Q8 (4 marks): (a) Sale: $480 \times 0.75 = \$360$. After markup: $360 \times 1.20 = \$432$ [2]. (b) No — $\$432 \neq \$480$ [1]. (c) The $25\%$ discount is on $\$480$ (savings $\$120$), but the $20\%$ markup is on the lower $\$360$ (only $\$72$). Different base prices mean the changes don't cancel — overall it's $\$48$ less, equivalent to a $10\%$ discount on the original [1].

Stretch Challenge · +25 XP, +10 coins

The Layered Sale

A store advertises “Up to $50\%$ off!”. The fine print: $20\%$ off, then a further $25\%$ at the till, then a final $15\%$ student discount. (a) Find the overall multiplier and the equivalent single percentage discount. (b) Is the “$50\%$ off” advertising honest?

Reveal solution

(a) Combined multiplier $= 0.80 \times 0.75 \times 0.85 = 0.510$. So the equivalent single discount is $1 - 0.510 = 49\%$. (b) Very nearly $50\%$ — just under. The ad is technically “up to”, which legally usually includes anything below, so it's arguable. The real saving is $49\%$, not the full $50\%$.

R
Quick Review

Three numbers

Marked, Sale, Discount

Forward

Sale = Marked × $(1-r)$

Reverse

Marked = Sale $\div (1-r)$

Find % off

Save/marked × 100

Sale $<$ Marked

Always

Sum check

Pay% + Off% = 100%

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