Jigsaw Puzzle Help I have a puzzle I'm trying to solve and I have all the border pieces set out but I'm pretty sure some are missing. How do I figure out how many pieces are in the border? It's a 1000 piece puzzle and the dimensions are 20" by 27".

If we assume that the number of pieces is exactly 1000, then we are looking for a divisor $d$ of $1000$ such that $d:\frac{1000}d\approx 20:27$. The closest approximation would obtained with $d=25$ ($25:40\approx 20:27$), so there'd be $4$ corner pieces and $2\cdot(25-2)+2\cdot(40-2)= 122$ other edge pieces.
But it is well possible that the number of total pieces is only approximately 1000 ...
With $999$ pieces, the same calculation arrives at $27:37\approx 20:27$ (where the approximation is much closer than above), so with this setup there'd be $4$ corner pieces and $2\cdot(27-2)+2\cdot(37-2)= 120$ other edge pieces.
