Question

The force needed to break a board varies inversely with its length. If Tom uses 20 lb of pressure to break a 1.5-ft board, how many po
essure would he need to use to break a 6 -board?​

Answer 1

If the force F and the length L are inversely proportional, then their product is constant:

$FL=k$

Given the values F=20 and L=1.5, we can deduce that the constant is

$20\cdot 1.5=30$

So, given L=6, we can solve for F as follows:

$6F=30 \iff F=5$