Source: Reader Jimmy Chng Gim Hong, citing a Chinese puzzle book.
Jospeh DeVincentis addressed the intended and extension solutions:
There are 40 total points, so the total points per subject X+Y+Z must be a factor of 40. If we assume all integer and no negative points, there must be a minimum of 3 points per subject, so the possible values are 4, 5, 8, 10, and 20 points per subject corresponding to 10, 8, 5, 4, and 2 subjects respectively. There cannot be only two subjects, because A's total of 22 would mean there were at least 11 points awarded for 1st place, but B got only 9 points. If there were four subjects (10 points each), A's total of 22 would mean that at least 6 points were awarded for first place. The possibilities that allow A a score of 22 are 6,4,0 and 7,2,1. Neither of these allows a score of eactly 9 points, however. If there were five subjects (8 points each), A's total of 22 would mean that at least 5 points were awarded for first place. The possibilities that allow A a score of 22 are 5,2,1; 6,2,0; and 7,1,0. The second case 6,2,0 does not allow a score of 9 points, but the others do, as 5+1+1+1+1 or 2+2+2+2+1 and as 7+1+1+0+0. Both of these give possible answers to the whole puzzle: A: 5+5+5+5+2 B: 1+1+1+1+5 C: 2+2+2+2+1 A: 7+7+7+1+0 B: 1+0+0+7+1 C: 0+1+1+0+7 With more than five subjects, there must be zero points for third place. We can have either 3,2,0 or 4,1,0 for 5 points per subject (8 subjects) or 3,1,0 for 4 points per subject (10 subjects). In all of these cases it's easy to find sets of results that work, for example: A: 3+3+3+3+3+3+2+2 B: 0+0+0+2+2+2+0+3 C: 2+2+2+0+0+0+3+0 A: 4+4+4+4+4+1+1+0 B: 0+0+0+0+0+4+4+1 C: 1+1+1+1+1+0+0+4 A: 3+3+3+3+3+3+1+1+1+1 B: 0+0+0+0+0+0+0+3+3+3 C: 1+1+1+1+1+1+3+0+0+0 Given these multiple solutions, it's most likely that a minimum of one point for Z was intended, making the first set of results the intended answer. 5 subjects, X=5, Y=2, Z=1. This also gives you a unique assignment of all the points: B got 5 in English and 1 in everything else, A got 2 in English and 5 in everything else, and C got 1 in English and 2 in everything else.