Q:

Find minimum planks for constructing surface

I have pieces of wooden planks 1.22m by 2.44m. I want to find the minimum number of planks required to construct a wooden surface of sides L length and W width.
The first intuition is that I can arrange the planks "horizontally" or "vertically" so I would calculate total number of planks N = (L/1.22 x W/2.44) or (L/2.44 x W/1.22) where the divisions needs to get rounded up to nearest integer. Since this is a simple case, I just calculate the two cases and get the minimum option.
For fun and interest, tried to express this in calculus but have failed. I don't know how to handle the discrete maths involved here. Anyone can advise or link to study material? Thanks.

A:

Calculate $n=\lceil \frac L{1.22}\rceil$ and $m=\lceil \frac W{1.22}\rceil$, whete $\lceil\ \rceil$ denotes rounding up. if at least one of $n,m$ is even, you need $\frac{nm}2$ planks. Otherwise you need $\frac{nm+\min\{n,m\}}2$ planks. If you are allowed to mix horizontal and vertical arrangement, then $\lceil \frac{nm}2\rceil$ planks are enough.

