Answer:
[tex]k=250[/tex]
Step-by-step explanation:
If y varies inversely with x, then
[tex]y=\dfrac{k}{x},[/tex]
where k is the constant of variation or the constant of inverse proportionality.
Since [tex]x=2.5[/tex] when [tex]y=100,[/tex] you have that
[tex]100=\dfrac{k}{2.5}[/tex]
Evaluate k:
[tex]k=100\cdot 2.5\\ \\k=250[/tex]
and
[tex]y=\dfrac{250}{x}[/tex]