Revelations xxi. (15)--“_And he that talked with me had a golden rule to measure the city and the gates thereof and the wall thereof_; (16) “_And the city lieth four square, and the length is as large as the breadth, and he measured the city with the reed twelve thousand furlongs. The length and the breadth and the height of it are equal._” 12,000 furlongs = 7,920,000 feet, which cubed = 496793088000000000000 cubic feet; half of this we will reserve for the Throne and Court of Heaven, and half the balance for streets, &c., leaving a remainder of 124198272000000000000 cubic feet. Divide this by 4096 (the cubic feet in a room 16 feet square) and there will be 3032184375 000000 rooms. Suppose that the world always did and always will contain 990,000,000 inhabitants, and that a generation lasts 33⅓ years, making in all 2,970,000,000 every century, and that the world will stand 100,000 years, totalling 2,970,000,000,000 inhabitants; then suppose there were 100 worlds equal to this in number of inhabitants and duration of years, making a total of 297,000,000,000,000 persons. There would then be more than 100 rooms 16 feet square for each person. 19. A man had a certain number of £’s, which he divided among 4 men. To the first he gave a part, to the second one-third of what was left after the first’s share, to the third he gave five-eighths of what was left, and to the fourth the balance, which equalled two-fifths of the first man’s share. How much money did he have, and how much did each receive, none receiving as much as £20? ROWING AGAINST TIME. 20. In a time race, one boat is rowed over the course at an average pace of 4 yards per second, another moves over the first half of the course at the rate of 3½ yards per second, and over the last half at 4½ yards per second, reaching the winning post 15 seconds later than the first. Find time taken by each. STOCK-BREEDING. 21. A farmer, being asked what number of animals he kept, answered: “They’re all horses but two, all sheep but two, and all pigs but two.” How many had he? A QUIBBLE. 22. What is the difference between twice one hundred and five, and twice one hundred, and ten? 23. The product of two numbers is six times their sum, and the sum of their squares is 325. What are the numbers? THE PUZZLE ABOUT THE “PER CENTS.” There are many persons engaged in business who often become badly mixed when they attempt to handle the subject of per centages. The ascending scale is easy enough: 5 added to 20 is a gain of 25%; given any sum of figures the doubling of it is an addition of 100%. But the moment the change is a decreasing calculation the inexperienced mathematician betrays himself, and even the expert is apt to stumble or go astray. An advance from 20 to 25 is an increase of 25%; but the reverse of this, that is, a decline from 25 to 20 is a decrease of only 20%.