A batch of bottles were packed in 25 boxes with 12 bottles in each box. If the same batch is packed using 20 bottles in each box, how many boxes would be filled?

Let the number of boxes be x.

Here, if the number of boxes increases, then the number of bottles will decrease.

So, it is inverse proportion.

Then, $25\times 12=x\times 20.$

$\Rightarrow x=\frac{25\times 12}{20}=15.$

Hence, 15 boxes will be filled.