Question

If y varies directly as x, and y=25 when x=5, find y when x=25

Answer 1

Answer:

The value of y is 125 when x=25.

Step-by-step explanation:

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

$y\propto x$

$y=kx$

Where k is constant of proportionality.

It is given that y=25 when x=5. Put x=5 and y=25 in the above equation to find the value of k.

$25=k(5)$

Divide both sides by 5.

$5=k$

The value of k is 5.

The relation between x and y is defined by the equation

$y=5x$

Put x=25 in the above equation.

$y=5(25)$

$y=125$

Therefore the value of y is 125 when x=25.

Answer 2

Answer:  The required value of y is 125.

Step-by-step explanation:  Given that the variable y varies directly as x. Also, y = 25 when x = 5.

We are to find the value of y when x = 25.

Given that y varies directly as x.

So, we have

$y\propto x\\\\\Rightarrow y=kx~~~~~~~~~~~\textup{[where k is the proportionality constant]}$

When x = 5, y = 25, then we have

$y=kx\\\\\Rightarrow 25=k\times5\\\\\Rightarrow k=\dfrac{25}{5}\\\\\Rightarrow k=5.$

So,

$y=kx\\\\\Rightarrow y=5x.$

Now, when x = 25, then the value of y will be

$y=5x=5\times25=125.$

Thus, the required value of y is 125.