Have I done this correctly?
f is inversely proportional to d
when d=50, f=256
Find value of f when d=80
Figured out a constant of 25/125
so
f=50/1*125/25=250
Is thsi correct?
f is inversely proportional to d ...
$\displaystyle f = \frac{k}{d}$
... where k is the constant of proportionality.
substitute in the given values to solve for k ...
$\displaystyle 256 = \frac{k}{50}$
$\displaystyle k = 50 \cdot 256 = 12800
$
$\displaystyle f = \frac{12800}{d}$
... finish the problem