Explanation:
first the theoretical maximum number :
the big block is 25cm×20cm×15cm.
so, the volume is 25×20×15 = 7500 cm³
we want to cut this note into pieces of 2.5cm×2cm×1cm with a volume of 2.5×2×1 = 5 cm³
so, we can get 7500/5 = 1500 such lumps out of the big block.
now, a quick check, if we can cut full pieces until the last bit, or if the shape of the big block will not allow us to fully cut it into the desired pieces, and we get some remains (too small to be lumps of the desired size and shape).
and we do this by checking, if each dimension of the big block can be divided by the dimensions of the small lumps without remainder (whole number results).
25 / 2.5 = 10, and no remainder here.
=> 10 cuts of 2.5 cm perpendicular to the length.
20 / 2 = 10, and no remainder here.
=> 10 cuts of 2cm perpendicular to the width.
15 / 1 = 15, and no remainder here.
=> 15 cuts of 1 cm perpendicular to the height.
so, yes, we can achieve the theoretical maximum number of 1500 lumps also in reality and cut the big block without remaining material into these small blocks.