Percentages (I) Form 1 Mathematics Chapter 3

Reminder Standard Homework (I) and (II) ▫Today! Standard Homework (III) and (IV) ▫28 Nov (Wed) Extra Tutorial ▫Today’s last CTP ▫MUST: 1, 10, 11, 12, 14, 16, 26, 30, 36 ▫Mon & Tue after-school – Consultation on G/F Open Book Quiz ▫28 Nov (Wed) Standard Homework (V) ▫30 Nov (Fri)

Percentage Increase (p.119) New value > Original value E.g. The Hang Seng Index increases from to We also say that the Index is increased by 5.65%.

Percentage Increase Last year, Andy was 150cm tall. His height is increased by 20% this year. What is his height now? Increase or Decrease? His height now is

Percentage Decrease (p.122) New value < Original value E.g. The price of a flat decrease from $2,200,000 to $1,804,000. We always say that the price of the flat is reduced by 18%.

Percentage Decrease The price of a car was $160,000 last month. What is the price of the car this month if the price is decreased by 15%? Increase or Decrease? The price this month is

Percentage Change (p.126) We can summarize the two formulae into one and call percentage change. If New value > Original value, then + (increase) If New value < Original value, then – (decrease)

Percentage Change The temperature was 30  C in the afternoon and the temperature dropped to 27  C in the evening. Find the percentage change in the temperature. The percentage change So, the percentage decrease in the temperature is 10%.

Percentage Change The profit of a company increases from $450,000 last year to $540,000 this year. What is the percentage change in profit? The percentage change So, the percentage increase in profit is 20%.

Time for Practice Page 127 of Textbook 1A ▫Class Practice Page 129 of Textbook 1A ▫Questions 6 – 14 Pages of WB 1A ▫Questions 3 - 9

Profit (p.131) Selling Price > Cost Price

Loss (p.134) Selling Price < Cost Price

Profit and Loss A shop sold a car at the profit % of 20%. If the profit was $32000, what was the cost of the car? What was the selling price? Profit or Loss? Let n be the Cost Price. Then, So, the Selling Price is

Time for Practice Pages of Textbook 1A ▫Class Practice Page 137 of Textbook 1A ▫Questions 7 – 19 Pages of WB 1A ▫Questions

Discount (p.138) Western style vs. Chinese style 88 折 = 12% off

Discount Western style vs. Chinese style 10% discount9 折 20% discount8 折 70% discount3 折 12% discount88 折 33% discount67 折 5% discount95 折

Discount Marked Price > Selling Price

Discount A pair of scorer shoes is sold at 25% discount at a marked price of $650. Can Vincent buy the shoes if he has $500? Marked price = $650 Selling price of the shoes Since Vincent got $500, he can buy the shoes.

Discount A golden ring is sold at 30% discount with a selling price of $441.What is the marked price? Selling price = $441. Let n be Marked price. Then, So, the Marked price is $630.

Time for Practice Page 141 of Textbook 1A ▫Class Practice Page 142 of Textbook 1A ▫Questions 3 – 10 Pages of WB 1A ▫Questions

Interest (p.144) When money is deposited in a bank, you will receive some Interest (I, 利息 ) according to the amount of Principal (P, 本金 ). The sum of P and I is called the Amount (A, 本利和 ). The interest is based on a percentage (r%, 利率 ) of the principal. It is normally given in a yearly basis, e.g. 5%p.a. (p.a. = “per annum”). There are two methods to find the interests: simple interest or compound interest.

Simple Interest Amount(A) = Principal(P) + Interest(I) Interest(I) = Principal(P)  Interest rate(r%)  period of time(T) Formula:

Simple Interest If $40000 is deposited in a bank for 5 years at 3%p.a., find the simple interest and the amount. P=$40000r=3T=5 (years) Simple interest (I) is So, the amount (A) is

Simple Interest How long will $20000 amount to $30000 at 5%p.a. simple interest? P=$20000r=5A=30000 I = $30000-$20000=$10000 Let T be the time. Then, The time required is 10 years.

Time for Practice Page 149 of Textbook 1A ▫Class Practice Page 150 of Textbook 1A ▫Questions 1 – 13 Pages of WB 1A ▫Questions 4 - 7

Reminder Standard Homework (I) and (II) ▫Today! Extra Tutorial ▫Today’s last CTP ▫MUST: 1, 10, 11, 12, 14, 16, 26, 30, 36 ▫Mon & Tue after-school – Consultation on G/F Open Book Quiz ▫28 Nov (Wed) Standard Homework (III), (IV) and (V) ▫30 Nov (Fri)

Enjoy the world of Mathematics!