Fifi indicated it: No. 71 of the collection of stickers known as Miscellaneous Review. It read as follows: 71. A laborer having built 105 rods of stone fence, found that if he had built 2 rods less a day he would have been 6 days longer in completing the job. How many rods a day did he build? Queed read this through once and announced: "He built seven rods a day." Fifi stared. "Why--how in the world, Mr Queed--" "Let us see if I am right. Proceed. Read me what you have written down." "Let _x_ equal the number of rods he built each day," began Fifi bravely. "Proceed." "Then _105_ divided by _x_ equals number of days consumed. And _105_ divided by _x - 2_ equals number of days consumed, if he had built _2_ rods less a day." "Of course." "And (_105_ ÷ _x - 2_) + _6_ = number of days consumed if it had taken him six days longer." "Nothing of the sort." Fifi coughed. "I don't see why, exactly." "When the text says 'six days longer,' it means longer than what?" "Why--longer than ever." "Doubtless. But you must state it in terms of the problem." "In terms of the problem," murmured Fifi, her red-brown head bowed over the bewildering book--"in terms of the problem." "Of course," said her teacher, "there is but one thing which longer can mean; that is longer than the original rate of progress. Yet you add the six to the time required under the new rate of progress." "I--I'm really afraid I don't quite see. I'm dreadfully stupid, I know--" "Take it this way then. You have set down here two facts. One fact is the number of days necessary under the old rate of progress; the other is the number of days necessary under the new rate. Now what is the difference between them?" "Why--isn't that just what I don't know?" "I can't say what you don't know. This is something that _I_ know very well." "But you know everything," she murmured. Without seeking to deny this, Queed said: "It tells you right there in the book." "I don't see it," said Fifi, nervously looking high and low, not only in the book but all over the room. The young man fell back on the inductive method: "What is that six then?" "Oh! _Now_ I see. It's the difference in the number of days consumed--isn't it?" "Naturally. Now put down your equation. No, no! The greater the rate of progress, the fewer the number of days. Do not attempt to subtract the greater from the less." Now Fifi figured swimmingly:-- (105/(x-2)) - (105/x) = 6 105x - 105x + 210 = 6x^2 - 12x 6x^2 - 12x - 210 = 0 6x^2 - 12x - 210 = 0 x^2 - 2x - 35 = 0 (x - 7) (X + 5) = 0 x = 7 or -5 She smiled straight into his eyes, sweetly and fearlessly. "Seven! Just what you said! Oh, if I could only do them like you! I'm ever and ever so much obliged, Mr. Queed--and now I can go to bed." Mr. Queed avoided Fifi's smile; he obviously deliberated.