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."