Building palisade with Lego bricks

I have problem solving the following questions:

  1. I have infinite amount of Lego bricks with 6 and 8 studs in length. I want to build a palisade that has the length of 48 studs . In what ways can I choose Lego bricks so that it fits perfectly?

  2. If I want to build a really long palisade, say 480 studs, in how many ways can I do that?

My thoughts: I came to the conclusion that (6 Lego bricks of 8 studs), (8 Lego bricks of 6 studs) and (3 Lego bricks of 8 studs and 4 Lego bricks of 6 studs) are the only ways to get a palisade that has the length of 48 studs. I don’t know if it requires calculation to get those numbers, I just made some tests and came up with these numbers.

I have 3 cases (see above) and somehow I think that I have to see/get a pattern out of these cases and that pattern should be recursive? (I think?)

I don’t know how to start solving this and I cant see any pattern from my cases. I have tried solving it as a diophantic equation but the results did not say me anything.

Any tips and advice will help!

Mathematics Asked on November 12, 2021

1 Answers

One Answer

The number of ways to partition $48$ into parts of size $6$ and $8$ is begin{eqnarray*} [x^{48}]: frac{1}{(1-x^6)(1-x^8)}. end{eqnarray*} To do $480$ just replace the $48$ in the above formula.

Alternatively, the solutions of the equation $6a+8b=48$ can be parameterised by $a=4t$ and $b=3(2-t)$, so $t$ can take any value from $0$ to $2$. So there are $3$ solutions.

Answered by Donald Splutterwit on November 12, 2021

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