F4 IGCSE Direct Proportion

Direct Proportion

F4 IGCSE Topic 7

Instruction

1. Independently study the new topic "direct proportion" with this Quizizz lesson.

2. ​Read the information provided carefully and write down anything important on your classwork book.

3. Solve the follow-up questions to check your learning progress.

4. Ask any questions to clarify your understanding.

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Objectives

• Understand the meaning of "direct proportion" through some examples.

• ​Learn how to mathematically express the relationship of two quantities which are directly proportional to each other.

• ​Solve problems by applying the knowledge acquired.

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​Direct Proportion

As one amount increases, another amount increases at the same rate.

​

​For example,

The number eggs required and the number of cookies you will make​

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​How much you earn and how many hours you work

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​The distance travelled at a constant speed and the time travelled

Multiple Select

Choose the option(s) that represent the direct proportional relationship.

• Temperature and the amount of heat

• Number of floors and the height of the building

• The amount of homework left and the time you spent on it

• The amount HK dollars you have and the amount of US dollars you will get after currency exchange

​Direct Proportion

​Direct Proportion

Multiple Select

If x and y are directly proportional to each other, then

• $$y=kx$$  

• $$y\propto x$$  

• $$y=x$$  

• $$y\propto k$$  

Multiple Choice

Which equation shows a direct proportion?

• y = 5x - 2

• y = $$\frac{3}{4}$$ x

• y - x = 4

• x = 6

Multiple Choice

Which equation is not an example of direct proportion?

• y = x

• y = 3x

• $$y=\frac{1}{5}x$$

• y = $$\frac{2}{3}$$ x + 5

Multiple Choice

What is the value of k in the following equation?

$$y=\frac{2}{7}x$$  

• 4

• $$-\frac{7}{2}$$  

• $$\frac{2}{7}$$  

• 7

Example 1:

If y is directly proportional to x and when y = 24, x = 6.

​Find the value of y when x = 10.

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​Step 1: Find k

Example 1:

If y is directly proportional to x and when y = 24, x = 6.

​Find the value of y when x = 10.

​

​Step 1: Find k Step 2: Use the equation to find the answer

Multiple Choice

Y is directly proportional to x. If y = 12 when x = 15, what is y when x = 20?

• 4/5

• 17

• 16

• 25

Multiple Choice

n varies directly with c. If c = 24 when n = 18, what is c when n = 22?

• $$\frac{88}{3}$$  

• 28

• $$\frac{33}{2}$$  

• 24

Multiple Choice

Upon seeing, "y varies directly as x" or "y is directly proportional to x" we immediately.....

• write down what x and y are

• write down what k is equal to

• substitute into the equation

• write y = kx

Multiple Choice

Y varies directly as x. If y = 39 when x = 52, what is the best answer for k?

• k = 52

• k = 4/3

• k = 3/4

• k = 39/52

Multiple Choice

If x = 9 when y = 30, and x = 27 when y = 90, is y directly proportional to x? If so, what is k equal to

• Yes, k = 10/3

• no

• Yes, k = 3/1

• Yes, k = 9

​Direct Proportion

Example 2:

If y is directly proportional to the square x and when y = 100, x = 2.

​Find the value of y when x = 3.

​

​Step 1: Find k

Example 2:

If y is directly proportional to the square x and when y = 100, x = 2.

​Find the value of y when x = 3.

​

​Step 1: Find k Step 2: Use the equation to find the answer

Multiple Choice

G is directly proportional to the square of H. When G = 80, H = 4. Find the value of G when H = 5.

• 125

• 5

• 25

• 100

Multiple Choice

J is directly proportional to the square of M. When J = 75, M = 5. Find the value of J when M = 4.

• 48

• 3

• 144

• 100

​Also write down the answers to the following two problems on your classwork book.

Draw

P is directly proportional to the cube of Q. When P = 500, Q = 5. Find the value of P when Q = 3

Draw

y is directly proportional to the square root of x. When y = 18, x = 144. Find the value of y when x = 100.

Poll

How do you feel about this topic of direct proportion?

• Very easy

• Very well understood

• Need more practice

• Difficult and need more help

Open Ended

Plenary: Create a real life problem related to two quantities that are directly proportional to each other.