Question

Suppose that y varies directly with x and y = 10 when x = 20. What is y when x = 15?

Answer 1

Given that,

y varies directly with x and y = 10 when x = 20.

To find,

The value of y when x = 15.

Solution,

$y\propto x\\\\y=kx$

Put x = 20 and y = 10

$k=\dfrac{y}{x}\\\\k=\dfrac{10}{20}\\\\=\dfrac{1}{2}$

Put k = 1/2 and x = 15 to find the value of y.

$y=\dfrac{1}{2}\times 15\\\\=7.5$

So, the value of y is 7.5