answer is right. Of the remaining 28, no less than 26 have sent in accidental solutions, and therefore fall short of the highest honours.
I will now discuss individual cases, taking the worst first, as my custom is.
Froggy gives no working—at least this is all he gives: after stating the given equations, he says "therefore the difference, 1 sandwich + 3 biscuits, = 3d.": then follow the amounts of the unknown bills, with no further hint as to how he got them. Froggy has had a very narrow escape of not being named at all!
Of those who are wrong, Vis Inertiæ has sent in a piece of incorrect working. Peruse the horrid details, and shudder! She takes x (call it " y ") as the cost of a sandwich, and concludes (rightly enough) that a biscuit will cost (3- y )/3. She then subtracts the second equation from the first, and deduces 3 y + 7 × (3- y )/3-4 y + 10 × (3- y )/3 = 3. By making two mistakes in this line, she brings out y = 2 ⁄ 2 . Try it again, oh Vis Inertiæ! Away with Inertiæ: infuse a little more Vis: and you will bring out the correct (though uninteresting) result, 0 = 0! This will show you that it is hopeless to try to coax any one of these 3 unknowns to reveal its separate value. The other competitor, who is wrong throughout, is either J. M. C. or T. M. C.: but, whether he be a Juvenile Mis-Calculator or a True Mathematician Confused, he makes the answers 7 d. and 1 s. 5 d. He assumes, with Too Much Confidence, that