Question

If f(x) varies directly with x and f(x) = 3 when x = 12, then what is the value of f(x) when x = 40?
480
160
10
4

Answer 1

HI!!

Answer 2

Uh Hey..

Answer 3

\(f(x)=3\) when \(x=12\) is a long winded way of saying
\[f(12)=3\]

Answer 4

and since it is "direct variation" then \[f(x)=kx\]
since
\[f(12)=k\times 12=3\] than means
\[k=\frac{3}{12}=\frac{1}{4}\]

Answer 5

now we know
\[f(x)=\frac{1}{4}x\] and so it is easy enough to find
\[f(40)\]