Question

If x and y vary directly, and x = 12 when y = 3, what will be the value of x when y = 9?

Answer 1

If you think about it, x=12 when y=3, right?
So the function is going to be f(x)=y*4
So, if y = 9 and you put it in the function, x is going to equal 36.
Do this help you understand?

Answer 2

Answer: The required value of x is 36.

Step-by-step explanation: Given that the variables x and y varies directly. Also, x = 12 when y = 3.

We are to find the value of x when y = 9.

Given that x and y varies directly. So, we have

`x\propto y\\\\\Rightarrow x=k~y,~~~~~~~~~~~~~~~~~~~~(i)`

where 'k' is the constant of proportionality.

Given that x = 12 when y = 3, so from equation (i), we have

`x=k~y\\\\\Rightarrow 12=k* 3\\\\\Rightarrow k=(12)/(3)\\\\\Rightarrow k=4.`

Substituting the value of k in equation (i), we have

`x=4y~~~~~~~~~~~~~~~~~~~~(ii)`

When y = 9, we get from equation (ii) that

`x=4* 9\\\\\Rightarrow x=36.`

Thus, the required value of x is 36.