Given:
w varies jointly as x and y.
w=10 when x=2 and y=1.
To find:
The value of w when x=4 and y=2.
Solution:
w varies jointly as x and y.
[tex]w\propto xy[/tex]
[tex]w=kxy[/tex] ...(i)
Where, k is the constant of proportionality.
w=10 when x=2 and y=1.
[tex]10=k(2)(1)[/tex]
[tex]10=2k[/tex]
[tex]\dfrac{10}{2}=k[/tex]
[tex]5=k[/tex]
The value of k is 5.
Putting k=5 in (i), we get
[tex]w=5xy[/tex]
To find the value of w when x=4 and y=2. Put x=4 and y=2.
[tex]w=5(4)(2)[/tex]
[tex]w=40[/tex]
Therefore, the value of w is 40 when x=4 and y=2.
