Answer
$\color{blue}{F=\dfrac{250}{d^2}}$
Work Step by Step
$F$ varies inversely with $d^2$, so the equation that represents the variation is:
$F=\dfrac{k}{d^2}$
Since $F=10$ when $d=5$ , substituting these into the tentative equation above gives:
$F=\dfrac{k}{d^2}
\\10=\dfrac{k}{5^2}
\\10=\dfrac{k}{25}
\\25(10) = \dfrac{k}{25} \cdot 25
\\250=k$
Thus, the equation of the inverse variation is:
$\color{blue}{F=\dfrac{250}{d^2}}$
