Inverse variation

[MathTutor]

Question: If 10 men can dig a hole in 2 days, how much time will 4 men take?

Answer: One man will take (10*2)= 20 days
            Four men will take 20/4= 5days.

Let y be the time taken and x be the number of man
y is inversely proportional to x.
y=k/x, where k is a constant.
when x=10, y=2, therefore k=2*10=20,
y=20/x
when x=4, y=20/4=5.