Combined Variation Review, Study notes of Mathematics

Translate a combined variation statement into an equation and solve it

Typology: Study notes

2019/2020

Uploaded on 12/05/2021

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Combined 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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Combined 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 combined variation statement into an equation and solve it.

Example

It is given that ๐‘Ž varies directly as ๐‘ and inversely as ๐‘. If ๐‘Ž = 16 when ๐‘ = 4 and ๐‘ = 3 , what is c when ๐‘Ž = 24 and ๐‘ = 6?

Combined Variation

Combined variation is a type of variation that describes direct and inverse variations in the same statement. Combined variation commonly stated as ' y varies directly as x and inversely as z '. It is written in equation form as ๐‘ฆ = ๐‘˜๐‘ฅ ๐‘ง , where k is the constant of proportionality.

Example

Step 2: Find the constant of proportionality ๐‘˜. Since ๐‘Ž = 16 , when ๐‘ = 4 and ๐‘ = 3. ๐‘Ž =

Example

Step 3: Rewrite the equation in Step 1 by substituting the value of k. Since ๐‘˜ = 12 and ๐‘Ž = ๐‘˜๐‘ ๐‘ , hence ๐‘Ž =

Activity 4

The volume V of wood in a tree varies directly as its height h and inversely as the square of its girth g. If the volume of a tree is 140 cubic meters if its height is 20 meters and its girth is 2 meters, what is the height of a tree with a volume of 500 cubic meters and a girth of 3 meters? Step 1: ๐‘‰ = ๐‘˜โ„Ž ๐‘” 2

Activity 4

Step 2: What is the value of k? If the volume of a tree is 140 cubic meters if its height is 20 meters and its girth is 2 meters. ๐‘‰ =

2 140 =

2

Activity 4

Step 3: From step 1 we have ๐‘‰ = ๐‘˜โ„Ž ๐‘” 2 and from step 2 we have ๐‘˜ = 28. Combining this we have ๐‘‰ =

2

Activity 4

What is the height of a tree with a volume of 500 cubic meters and a girth of 3 meters? Step 4: Find the unknown by substituting to the equation in Step 3. ๐‘‰ =

2 500 =

2

Key point

  • Combined variation is a type of variation that describes direct and inverse variations in the same statement.

Quiz

Solve the ff.

  1. If r varies directly as s and inversely as the square of u , and ๐‘Ÿ = 2 when ๐‘  = 18 and ๐‘ข = 2 , find: a. r when ๐‘ข = 3 and ๐‘  = 27. b. s when ๐‘ข = 2 and ๐‘Ÿ = 4. c. u when ๐‘Ÿ = 1 and ๐‘  = 36.

Additional Activities

Solve the following:

  1. w varies directly as x and y and inversely as ๐‘ฃ 2 and ๐‘ค = 1200 when ๐‘ฅ = 4 , ๐‘ฆ = 9 and ๐‘ฃ = 6. Find w when ๐‘ฅ = 3 , ๐‘ฆ = 12 , and ๐‘ฃ = 9.
  2. Suppose p varies directly as ๐‘ 2 and inversely as ๐‘  3 . If ๐‘ = 3 4 when ๐‘ = 6 and ๐‘  = 2 , find b when ๐‘ = 6 and ๐‘  = 4.

Reference

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