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Joint Variation: Group 3

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JOINT VARIATION

Group 3
What is Joint Variation?
•  Joint Variation refers to a scenario in which the
value of one variable depends on two, or more,
other variables when the other variables are held
constant.
 y = kx
'' y varies jointly as x and z ''
''y is proportional to x and z''
2
                                                                        

Translate each statement into a mathematical sentence.


 1.) P varies jointly as q and r. 
                     P= kqr
 2.) V varies jointly as 1, w and h.
                    V=kLwh
  3) The electrical voltage V varies jointly as the current I and
   the resistance R.
                     V=kIR
Solve for the constant k, then find the missing value. Z varies
jointly as x and y and z = 60 , when x = 5 and y = 6.

a) Find z when x = 7 and y = 6    b) Find x when 3 = 72 and y = 4


     Z=kyx         k=2 
 z = 2xy  z = 2xy
 z = 2(7)(6) 72 = 2x(4)
 z = 84 72/8 = 8x/8
     9 = x
Examples;

1. Find the equation of variation where  a varies jointly as b and c, and 


a=36  when  b=3  and  c=4.

a = kbc a = 36  b = 3 c = 4

36 = k(3)(4) a = 3bc – equation of variation 


36 = 12k
36/12 = 12k/12
  3=k
Examples;
2. Z varies jointly as x and y. If z = 60 when x = 5 and y = 6, find z when x
= 7 and y = 6.

z = kxy  z = 60 y = 6 x = 5 z = 2xy             x = 7 y = 6
60 = k(5)(6)  z = 2(7)(6)
60 = 30k  z = 84
60/30 = 30k/30
    2=k
1. The variable x is in joint variation with y and z. When the values of y and z are
4 and 6, x is 16. What is the value of x when y = 8 and z =12?

Solution: 
The equation for the given problem of joint variation is  x = Kyz where K is
the constant.

For the given data 16 = K × 4 × 6  or, K = 46.

So substituting the value of K the equation becomes  x = 4yz/6

Now for the required condition  x = 4×8×126  = 64

 Hence the value of x will be 64. 


2. A is in joint variation with B and square of C. When A = 144, B = 4 and C = 3.
Then what is the value of A when B = 6 and C = 4? 

Solution: 
From the given problem equation for the joint variation is A = KBC2 

From the given data value of the constant K is K = BC2A K = 4×3^21/44 = 36/144 = 
¼.
Substituting the value of K in the equation A = BC24 A = 6×424 = 24
3. The area of a triangle is jointly related to the height and the base of the
triangle. If the base is increased 10% and the height is decreased by 10%, what
will be the percentage change of the area? 

Solution:
We know the area of triangle is half the product of base and height. So the joint 
variation equation for area of triangle is A = bh2bh2 where A is the area, b is
the base and h is the height. Here 1212 is the constant for the equation. 
Base is increased by 10%, so it will be b x 110100110100 = 11b1011b10.
 Heightis decreased by 10%, so it will be h x 9010090100 = 9h109h10. So
the new area after the changes of base and height is 11b10×9h10211b10×9h102
= (9910099100)bh2bh2 = 9910099100A. So the area of the triangle is decreased
by 1%.
4. A rectangle’s length is 6 m and width is 4 m. If length is doubled and width is halved, how much the
perimeter will increase or decrease? 

Solution:
Formula for the perimeter of rectangle is P = 2(l + w) where P is perimeter, l is length and w is width.

This is joint variation equation where 2 is constant. 

So P = 2(6 + 4) = 20 m

If length is doubled, it will become 2l. 

And width is halved, so it will become w2.

So the new perimeter will be P = 2(2l + w2) = 2(2 x 6 + 42) = 28 m.

So the perimeter will increase by (28 - 20) = 8 m.


LET'S TRY THIS!
1.  a varies jointly as b and c.
 a = k b c
2. h is jointly proportional to i and j.
 h = k i j

3. m varies jointly as n and p.


m=knp
4. s is jointly proportional to t and v.
s=ktv
   THANK YOU!!!

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