Question

If y varies directly with x, find the value of y when x = 27 for the direct variation with the given information. y = 7 when x = -9 y =​

Answer 1

Given:

y varies directly with x,

It is given that y = 7 when x = -9.

To find:

The value of y when x = 27 for the direct variation.

Solution:

It is given that y varies directly with x, so

$y\propto x$

$y=kx$             ...(i)

Where, k is the constant of proportionality.

It is given that y = 7 when x = -9. Putting these values in (i), we get

$7=k(-9)$

$-\dfrac{7}{9}=k$

Putting $k=-\dfrac{7}{9}$ in (i), we get

$y=-\dfrac{7}{9}x$

Putting $x=27$,  we get

$y=-\dfrac{7}{9}(27)$

$y=-21$

Therefore, the required value is $y=-21$.