Question

If y varies directly as x and y is 18 when x is 5 which expression can be used to find the value of y when x is 11?

Answer 1

y = kx  where k is a constant   Thats direct variation.

plug in given values:-

18  = k * 5

k = 18/5 = 3.6

so the equation of variation is y = 3.6x

when x = 11, y = 3.6 * 11 =  39.6  Answer

Answer 2

Answer:

The value of y is $\frac{198}{5}$ or 39.6.

Step-by-step explanation:

It is given that y varies directly as x and y. It means y is directly proportional to x.

$y\propto x$

$y=kx$            .... (1)

where, k is constant of proportionality.

It is given that y is 18 when x is 5.

Substitute y=18 and x=5 in equation (1).

$18=k(5)$

Divide both sides by 5.

$\frac{18}{5}=k$

The value of k is $\frac{18}{5}$. So, the relation between x and y is

$y=\frac{18}{5}x$            .... (2)

We need to find the value of y when x=11.

$y=\frac{18}{5}(11)$

$y=\frac{198}{5}$

$y=39.6$

Therefore the value of y is $\frac{198}{5}$ or 39.6.