Answer:
constant of variation(k) is, 250.

Step-by-step explanation:
The inverse variation says that:

then, the equation is in the form of :
....[1] where, k is the constant of variation
As per the statement:
Suppose that y varies inversely with x.
then,
by definition of inverse variation we have;

When x = 2.5 and y = 100 then
Substitute these in [1] we have;

Multiply 2.5 both sides we have;

or
k = 250
⇒
Therefore, the constant of variation is, 250 and the equation we get 