Question

If f(x) varies directly with x and f(x) = 4 when x = 12, then what is the value of f(x) when x = 60?

Answer 1

ANSWER

$f(60)=3\times60=180$

EXPLANATION
We were given that
$f(x)$
varies directly as
$x.$

We can write this mathematically as,

$f(x) \propto \: x.$

This implies that,

$f(x) = kx$
where k is the constant of variation.

$f(4)=4k$

This implies that,

$4k=12$

$k = 3$

The equation becomes

$f(x)=3x$

When $x=60$

$f(60)=3\times60=180$