Joint Variation: Solving Problems Involving Joint Variations, Study notes of Mathematics

A step-by-step solution to translating joint variation statements into equations and finding the unknown variable. It includes examples and activities in various contexts, such as physics and chemistry. Students will learn how to determine the constant of proportionality and use it to find the unknown variable.

Typology: Study notes

2019/2020

Uploaded on 12/05/2021

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Joint Variation
Presented by:
Paul Jorel R. Santos
Overview of
DepEd MIS
and BEIS
Republic of the Philippines
Department of Education
Region IV โ€“A (CALABARZON)
City Schools Division of Dasmariรฑas
DASMARIร‘AS NATIONAL HIGH SCHOOL
Congressional South Ave. Burol I, Dasmariรฑas City
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Joint Variation

Presented by: Paul Jorel R. Santos

view of

d MIS

BEIS

Republic of the Philippines Department of Education Region IV โ€“ A (CALABARZON) City Schools Division of Dasmariรฑas DASMARIร‘AS NATIONAL HIGH SCHOOL Congressional South Ave. Burol I, Dasmariรฑas City

Objective

Translate a joint variation statement into an equation and solve it.

Example

a varies jointly as b and c. If ๐‘Ž = 18 when ๐‘ = 2 and ๐‘ = 3 , what is b if ๐‘Ž = 24 when ๐‘ = 6?

Joint Variation

Joint variation is a type of variation that describes two direct variations in one statement. The variation statement ' y varies jointly as x and z ' is written in equation form as ๐‘ฆ = ๐‘˜๐‘ฅ๐‘ง.

Example

a varies jointly as b and c. If ๐‘Ž = 18 when ๐‘ = 2 and ๐‘ = 3 , what is b if ๐‘Ž = 24 when ๐‘ = 6? Step 2: Find the constant of proportionality. Since ๐‘Ž = 18 , when ๐‘ = 2 and ๐‘ = 3. 18 = ๐‘˜( 2 )( 3 ) 18 = 6๐‘˜ ๐‘˜ = 3

Example

a varies jointly as b and c. If ๐‘Ž = 18 when ๐‘ = 2 and ๐‘ = 3 , what is b if ๐‘Ž = 24 when ๐‘ = 6? Step 3: Rewrite the equation in Step 1 by substituting the value of k. Since ๐‘˜ = 3 and ๐‘Ž = ๐‘˜๐‘๐‘, hence ๐‘Ž = 3๐‘๐‘

Activity 3

In chemistry, the absolute temperature T of a perfect gas varies jointly as its pressure P and its volume V. At 400K, the pressure of the gas is 40 pounds per square inch (psi) and the volume is 100 cubic inches. Find the volume of the gas at 700 K when its pressure is 50 psi. Step 1: Write the correct equation. ๐‘‡ = ๐‘˜๐‘ƒ๐‘‰

Activity 3

Step 2: Find the constant of proportionality. Since ๐‘‡ = 400๐พ, when ๐‘ƒ = 40๐‘๐‘ ๐‘– and ๐‘‰ = 100๐‘๐‘ข. ๐‘–๐‘› ๐‘‡ = ๐‘˜๐‘ƒ๐‘‰ 400 = ๐‘˜( 40 )( 100 ) 400 = 4000๐‘˜ ๐‘˜ =

Activity 3

Step 4: Find the unknown by substituting to the equation in Step 3. ๐‘‡ =

The volume of the gas is 140 cubic inches.

Tips

  • If you are solving for k in the equation ๐‘ฆ = ๐‘˜๐‘ฅ๐‘ง, simply multiply the values of x and z , then divide y by the product. Alternatively, you may divide y by either of the two variables, then divide the quotient by the other variable.

Quiz 3

Solve for the indicated variable in each of the following.

  1. If z varies jointly as x and y , z is 2 when ๐‘ฅ = 4 and ๐‘ฆ = 3. What is z if ๐‘ฅ = 8 and ๐‘ฆ = 6?
  2. The area A of a triangle varies jointly as its base b and height h. The area is 100 sq. units when the base is 10 units and the height is 20 units. What is the base if the area is 200 sq units and the height is 25 units?

Additional Activities

Solve the following:

  1. The amount of gasoline used by a car varies jointly as the distance travelled and the square root of the speed. Suppose a car used 25 liters on a 100 kilometer trip at 100 km/hr. About how many liters will it use on a 192 kilometer trip at 64 km/hr.?

Reference

  • www.school.quipper.com
  • Grade 9 Mathematics Learnerโ€™s Material