A Tangled Tale : Knot Four : Answer

Problem. --There are 5 sacks, of which Nos. 1, 2, weigh 12 lbs.; Nos. 2, 3, 13 1/2 lbs.; Nos. 3, 4, 11 1/2 lbs.; Nos. 4; 5, 8 lbs.; Nos. 1, 3, 5, 16 lbs. Required the weight of each sack.

Answer.--5 1/2, 6 1/2, 7, 4 1/2, 3 1/2.

The sum of all the weighings, 61 lbs., includes sack No. 3 thrice and each other twice. Deducting twice the sum of the 1st and 4th weighings, we get 21 lbs. for thrice No. 3, i.e. 7 Ibs. for No. 3. Hence, the 2nd and 3rd weighings give 6 1/2 lbs., 4 1/2 lbs. for Nos. 2, 4; and hence again, the 1st and 4th weighings give 5 1/2 lbs.,3 1/2 lbs., for Nos. 1, 5.

Ninety-seven answers have been received. Of these, 15 are beyond the reach of discussion, as they give no working. I can but enumerate their names, and I take this opportunity of saying that this is the last time I shall put on record the names of competitors who give no sort of clue to the process by which their answers were obtained. In guessing a conundrum, or in catching a flea, we do not expect the breathless victor to give us afterwards, in cold blood, a history of the mental or muscular efforts by which he achieved success; but a mathematical calculation is another thing. The names of this "mute inglorious" band are Common Sense, D. E. R., Douglas, E. L., Ellen, I. M. T., J. M. C., Joseph, Knot I, Lucy, Meek, M. F. C., Pyramus, Shah, Veritas.

Of the eighty-two answers with which the working, or some approach to it, is supplied, one is wrong: seventeen have given solutions which are (from one cause or another) practically valueless: the remaining sixty-four I shall try to arrange in a Class List, according to the varying degrees of shortness and neatness to which they seem to have attained.

The solitary wrong answer is from Nell. To be thus "alone in a crowd" is a distinction--a painful one, no doubt, but still a distinction. I am sorry for you, my dear young lady, and I seem to hear your tearful exclamation, when you read these lines, "Ah! This is the knell of all my hopes!" Why, oh why, did you assume that the 4th and 5th bags weighed 4 lbs. each? And why did you not test your answers? However, please try again: and please don't change your nom-de-plume: let us have Nell in the First Class next time!

The seventeen whose solutions are practically valueless are Ardmore, A Ready Reckoner, Arthur, Bog-Lark, Bog-Oak, Bridget, First Attempt, J. L. C., M. E. T., Rose, Rowena, Sea-Breeze, Sylvia, Thistledown, Three-Fifths Asleep, Vendredi, and Winifred. Bog-Lark tries it by a sort of "rule of false", assuming experimentally that Nos. 1, 2, weigh 6 lbs. each, and having thus produced 17 1/2 instead of 16, as the weight of 1, 3, and 5, she removes "the superfluous pound and a half", but does not explain how she knows from which to take it. Three-Fifths Asleep says that (when in that peculiar state) "it seemed perfectly clear" to her that, "3 out of the 5 sacks being weighed twice over, 3/5 of 45=27, must be the total weight of the 5 sacks." As to which I can only say, with the Captain, "it beats me entirely!" Winifred, on the plea that "one must have a starting-point", assumes (what I fear is a mere guess) that No. 1 weighed 59 lbs. The rest all do it, wholly or partly, by guess-work.

The problem is of course (as any algebraist sees at once) a case of "simultaneous simple equations" It is, however, easily soluble by arithmetic only; and, when this is the case, I hold that it is bad workmanship to use the more complex method. I have not, this time, given more credit to arithmetical solutions; but in future problems I shall (other things being equal) give the highest marks to those who use the simplest machinery. I have put into Class I those whose answers seemed specially short and neat, and into Class III those that seemed specially long or clumsy. Of this last set, A. C. M., Furze-Bush, James, Partridge, TC. W., and Waiting for the Train, have sent long wandering solutions, the substitutions have no definite method, but seeming to have been made to see what would come of it. Chilpome and Dublin Boy omit some of the working. Arvon Marleborough Boy only finds the weight of one sack.