If Y varies inversely as x, then as y increases, x decreases or vice versa. It can be represented by an equation as:
y α 1/x
We add a proportionality constant k in order to change it to an equality.
y = k/x
We then solve for k by substituting the first condition to the equation.
y = k/x
50 = k/10
k = 500
When x = 20, then:
y = 500/x
y = 500/20
y = 25