In kickboxing, it is found that the force needed to break a board , varies inversely with the length of the board. If it takes 5 pounds of pressure to break a board 2 feet long, how many pounds of pressure will it take to break a board that is 8 feet long?

It will take 1.25 pounds of pressure to break a board that is 8 feet long.

Explanation:

Let the force needed be F
Let the length of the board be L

Since F varies inversely as L,
F = k/L

When F = 5 and L = 2,
5 = k/2
k = 10

When L = 8,
F = 10/8
F = 1.25 pounds of pressure