Given that,
y varies directly with x and y = 10 when x = 20.
To find,
The value of y when x = 15.
Solution,
[tex]y\propto x\\\\y=kx[/tex]
Put x = 20 and y = 10
[tex]k=\dfrac{y}{x}\\\\k=\dfrac{10}{20}\\\\=\dfrac{1}{2}[/tex]
Put k = 1/2 and x = 15 to find the value of y.
[tex]y=\dfrac{1}{2}\times 15\\\\=7.5[/tex]
So, the value of y is 7.5
