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14-Jun-14Created by Mr. Lafferty Maths Dept. Direct Proportion www.mathsrevision.com Direct Proportion Graphs Direct Proportion formula and calculations.

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Presentation on theme: "14-Jun-14Created by Mr. Lafferty Maths Dept. Direct Proportion www.mathsrevision.com Direct Proportion Graphs Direct Proportion formula and calculations."— Presentation transcript:

1 14-Jun-14Created by Mr. Lafferty Maths Dept. Direct Proportion Direct Proportion Graphs Direct Proportion formula and calculations Inverse Direct Proportion Direct Proportion Other Direct Proportion formula

2 14-Jun-14Created by Mr. Lafferty Maths Dept. Starter Questions Starter Questions

3 14-Jun-14Created by Mr. Lafferty Maths Dept. Learning Intention Success Criteria 1.To explain the term Direct Proportion. 1. Understand the idea of Direct Proportion. Direct Proportion 2. Solve simple Direct Proportional problems. Direct Proportion

4 14-Jun-14Created by Mr. Lafferty Maths Dept. Direct Proportion.. When you double the number of cakes you double the cost. CakesCost Two quantities, (for example, number of cakes and total cost) are said to be in DIRECT Proportion, if : Direct Proportion Example :The cost of 6 cakes is £4.20. find the cost of 5 cakes ÷ 6 = x 5 = £3.50 Write down two quantities that are in direct proportion.

5 14-Jun-14Created by Mr. Lafferty Maths Dept. Direct Proportion £$ Example :On holiday I exchanged £30 for $45. How many $ will I get for £ ÷ 3 0 = x 50 = $75 What name do we give to this value Exchang e rate

6 14-Jun-14Created by Mr. Lafferty Maths Dept. Direct Proportion (a)Simply multiple by 2 : Example :To make scrambled eggs for 2 people we need 2eggs, 4g butter and 40 ml of milk. How much of each for (a)4 people(b)Just himself 4 eggs, 8g butter, 80 ml of milk. (b)Simply half original amounts: 1 eggs, 2g butter, 20 ml of milk.

7 14-Jun-14Created by Mr. Lafferty Maths Dept. Now try Exercise 1 Ch8 (page 101) Direct Proportion

8 14-Jun-14Created by Mr. Lafferty Maths Dept. Starter Questions Starter Questions

9 14-Jun-14Created by Mr. Lafferty Maths Dept. Learning Intention Success Criteria 1. To explain how Direct Direct Proportion Graph is always a straight line. 1. Understand that Direct Proportion Graph is a straight line. Direct Proportion 2. Construct Direct Proportion Graphs. Direct Proportion Graphs

10 14-Jun-14Created by Mr. Lafferty Maths Dept. Direct Proportion The table below shows the cost of packets of Biscuits. Direct Proportion Graphs We can construct a graph to represent this data. What type of graph do we expect ?

11 14-Jun-14Created by Mr. Lafferty Maths Dept. Direct Proportion Graphs Notice that the points lie on a straight line passing through the origin This is true for any two quantities which are in Direct Proportion.

12 14-Jun-14Created by Mr. Lafferty Maths Dept. Direct Proportion Direct Proportion Graphs KeyPoint Two quantities which are in Direct Proportion always lie on a straight line passing through the origin.

13 14-Jun-14Created by Mr. Lafferty Maths Dept. Direct Proportion Example : Plot the points in the table below. Are they in Direct Proportion? Direct Proportion Graphs We plot the points (1,3), (2,6), (3,9), (4,12)X1234y36912

14 14-Jun-14Created by Mr. Lafferty Maths Dept. 1 Direct Proportion Plotting the points (1,3), (2,6), (3,9), (4,12) Direct Proportion Graphs Since we have a straight line passing through the origin x and y are in Direct Proportion. x y

15 14-Jun-14Created by Mr. Lafferty Maths Dept. 1 Direct Proportion Find the formula connecting y and x. Direct Proportion Graphs Formula has the form : x y Gradient = 3 Formula is :y = 3x y = kx

16 14-Jun-14Created by Mr. Lafferty Maths Dept. Direct Proportion Direct Proportion Graphs Key point of Ex 2 Fill in table Find gradient from graph Write down formula using knowledge from straight line chapter

17 14-Jun-14Created by Mr. Lafferty Maths Dept. Now try Exercise 2 Ch8 (page 104) Direct Proportion

18 14-Jun-14Created by Mr. Lafferty Maths Dept. Starter Questions Starter Questions

19 14-Jun-14Created by Mr. Lafferty Maths Dept. Learning Intention Success Criteria 1. To explain how to work out Direct Proportion formula. 1. Understand the process for calculating direct proportion formula. Direct Proportion 2. Calculate gradient from information given. Direct Proportion Formula

20 14-Jun-14Created by Mr. Lafferty Maths Dept. Direct Proportion Q. Given that y is directly proportional to x, and when y = 20, x = 4. Find a formula connecting y and x Direct Proportion Formula Since y is directly proportional to x the formula is of the form y = kx k is the gradient 20 = k(4) k = 20 ÷ 4 = 5 y = 5x

21 14-Jun-14Created by Mr. Lafferty Maths Dept. Direct Proportion Q. The number of dollars (d) varies directly as the number of £s (P). You get 3 dollars for £2. Find a formula connecting d and P. Direct Proportion Formula Since d is directly proportional to P the formula is of the form d = kP k is the gradient 3 = k(2) k = 3 ÷ 2 = 1.5 d = 1.5P

22 14-Jun-14Created by Mr. Lafferty Maths Dept. Direct Proportion Q. How much will I get for £20 Direct Proportion Formula d = 1.5P d = 1.5 x 20 = 30 dollars

23 14-Jun-14Created by Mr. Lafferty Maths Dept. Exercise 3 Ch8 (page 105) Direct Proportion Direct Proportion Formula

24 14-Jun-14Created by Mr. Lafferty Maths Dept. Starter Questions Starter Questions

25 14-Jun-14Created by Mr. Lafferty Maths Dept. Learning Intention Success Criteria 1. To explain how to work out harder Direct Proportion formula. 1. Understand the process for calculating direct proportion formula. Direct Proportion 2. Calculate k for harder direct proportion formula. Harder Direct Proportion Formula

26 14-Jun-14Created by Mr. Lafferty Maths Dept. Direct Proportion Q. Given that y is directly proportional to the square of x, and when y = 40, x = 2. Find a formula connecting y and x when. Since y is directly proportional to x squared the formula is of the form y = kx 2 40 = k(2) 2 k = 40 ÷ 4 = 10 y = 10x 2 Harder Direct Proportion Formula y x

27 14-Jun-14Created by Mr. Lafferty Maths Dept. Direct Proportion Q. Calculate y when x = 5 y = 10x 2 y = 10(5) 2 = 10 x 25 = 250 Harder Direct Proportion Formula y x

28 14-Jun-14Created by Mr. Lafferty Maths Dept. Direct Proportion Q. The cost (C) of producing a football magazine varies as the square root of the number of pages (P). Given 36 pages cost 45p to produce. Find a formula connecting C and P. Since C is directly proportional to square root of P the formula is of the form k = 48 ÷ 6 = 8 Harder Direct Proportion Formula y x

29 14-Jun-14Created by Mr. Lafferty Maths Dept. Direct Proportion Q. How much will 100 pages cost. Harder Direct Proportion Formula y x

30 14-Jun-14Created by Mr. Lafferty Maths Dept. Exercise 4B Ch8 (page 106) Direct Proportion Harder Direct Proportion Formula

31 14-Jun-14Created by Mr. Lafferty Maths Dept. Starter Questions Starter Questions

32 14-Jun-14Created by Mr. Lafferty Maths Dept. Learning Intention Success Criteria 1. To explain the term Inverse Proportion. 1. Understand the idea of Inverse Proportion. Inverse Proportion 2. Solve simple inverse Proportion problems. Inverse Proportion

33 14-Jun-14Created by Mr. Lafferty Maths Dept. Inverse Proportion Inverse Proportion is when one quantity increases and the other decreases. The two quantities are said to be INVERSELY Proportional or (INDIRECTLY Proportional) to each other. Example :Fill in the following table given x and y are inversely proportional. Inverse ProportionX1248y y x

34 14-Jun-14Created by Mr. Lafferty Maths Dept. Inverse Proportion MenHours Inverse Proportion is the when one quantity increases and the other decreases. The two quantities are said to be INVERSELY Proportional or (INDIRECTLY Proportional) to each other. Example :If it takes 3 men 8 hours to build a wall. How long will it take 4 men. (Less time !!) x 8 = 24 hours 4 24 ÷ 4 = 6 hours Inverse Proportion y x

35 14-Jun-14Created by Mr. Lafferty Maths Dept. Inverse Proportion MenMonths Example :It takes 10 men 12 months to build a house. How long should it take 15 men x 10 = ÷ 15 = 8 months Inverse Proportion y x

36 14-Jun-14Created by Mr. Lafferty Maths Dept. Inverse Proportion SpeedTime Example : At 8 m/s a journey takes 32 minutes. How long should it take at 10 m/s mins 1 32 x 8 = 256 mins ÷ 10 = 25.6 mins Inverse Proportion y x

37 14-Jun-14Created by Mr. Lafferty Maths Dept. Exercise 5 Ch8 (page 108) Inverse Proportion


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