This one is quite tough,

You can't do (40 x 30 x 20) / (5 x 3 x 3) because the blocks are fixed solids.

A simple idea is, how many 2 x 2 squares can you draw within a single 3 x 3 square? Even though (3 x 3) / (2 x 2) = 2.25, which suggests 2 squares, we can actually only draw 1 square because the remaining spaces do not allow squares of size 2 x 2 to be drawn.

Here, 530 squares is already very difficult to attain, considering that (40 x 30 x 20) / (5 x 3 x 3) = 533 is the absolute maximum, but I doubt you can hit 533 because of the spacings.

The answer isnt 520?

530 is surprisingly possible.

520 is easy, but 530 requires greater in depth thinking.

I think the setter didn’t expect 530 to be possible.

This is more of an IQ question than a P6 question.

The setter intended you to do 20/5 x 30/3 x (40/3, rd down) to get 520.

But no one said that I cannot arrange them in other manners.

What I will first do is this. Using a space of 40 cm by 30 cm by 15 cm (I used 15 cm out of a length of 20 cm), I arrange the blocks in a 5-3-3 configuration.

This requires (40/5) x (30/3) x (15/3) = 400 blocks.

For the remaining 40 cm by 30 cm by 5 cm space, I arrange them in a 3-3-5 configuration instead.

This would be (40/3, rd down) x (30/3) x (5/5), or a further 130 blocks.

For a total of 530 blocks.