A cuboidal wooden block 25 cm long, 20 cm wide and 12 cm high stands on a table. Every face is polished except the one resting on the table. What area is polished, in square cm?

All six faces come to 2(lb + bh + hl) = $2(25\times 20+20\times 12+12\times 25)=2(500+240+300)=2080$ sq cm. The hidden face is the 25 by 20 base, 500 sq cm, so the polished area = 2080 - 500 = 1580 sq cm. The trap 2080 polishes everything, including the face on the table; 1080 removes the top as well as the bottom, but only the bottom is hidden; 1040 is the bracket 500 + 240 + 300 with the factor 2 never applied.