Yeah I think the examples given are probably examples of hard exercises or the grades are a poor translation (maybe grade 1 has 6 year olds, for example.) Anot

Yeah I think the examples given are probably examples of hard exercises or the grades are a poor translation (maybe grade 1 has 6 year olds, for example.) Another solution is with geometry: Start with a 1x1x1 cube of coffee. Remove top half and replace with milk. Now remove left third of resulting combined shape (leaving a 2/3 x 1/2 x 1 cuboid of coffee). Now remove front sixth (leaving a 2/3 x 1/2 x 5/6 cuboid). Now drink it all. Now add up the volumes of the shape and write down the answer.