Question

If f(x) varies directly with x and f(x)= 70 when x=5 , find the value of f(x) when x=9.XRound you final answer to the nearest whole number.

Answer 1

Since f(x) varies directly with x, we can write

`f(x)=k\cdot x`

where k is the constant of proportionality. We know that when x=5, f(5)=70, then we have

`70=k\cdot5`

then, k is given as

`\begin{gathered} k=(70)/(5) \\ k=14 \end{gathered}`

Then, the equation which model the problem is

`f(x)=14x`

Now, we can substitute x=9 into this result. It yields,

`\begin{gathered} f(9)=14(9) \\ f(9)=126 \end{gathered}`

Therefore, the answer is 126