15. How many pounds in a kilo, when a cubic foot of water weighs 1,000 oz.? (See problem 10.)

16. What would be the circumference of the earth in miles if the meter measured 40 inches?

(The meter is Tooooooo of what part of circumference ?)

17. How many square yards in a square meter?

18. How many acres in a hectare? (See problem 4.)

19. How many rods in a hectometer?

20. How many cubic feet in a stere? (See problem 6.)

21. How many troy grains (7,000 to av. lb.) in a gram? (See problem 15.)

22. How many kilometers in a mile?

1188. The square meter is the principal unit of surfaces, such as walls, ceilings, floors, etc.

100 centiares (ca.) = 1 are (a.) = 119.6 sq. yd.

1189. The are is the principal unit of surface of small plots of land. The area of a farm is expressed in hectares, of a country in square kilo

1192. The stere (cubic meter) is used for measuring wood.

10 decisteres (dst.) = 1 stere (st.) = 35.316 cu. ft.

1194. The liter and the hectoliter are the principal units.

1196. The kilo is the ordinary unit. Heavy articles are sold by the

tonneau.

CHAPTER XV.

ALGEBRAIO EQUATIONS.-TWO UNKNOWN QUANTITIES. THREE UNKNOWN QUANTITIES.—PURE QUADRATIOS.— AFFECTED QUADRATICS.

1200. In the quantities 2a, 3x, 5xy, 15 abc, the numbers 2, 3, 5, 15, are called coefficients. When no coefficient is expressed, 1 is understood. Thus, abc1abc.

Where no sign is expressed, + is understood.

1201. What a person has may be represented with a plus sign (+) placed before the amount; debts may be shown by a minus sign (-) placed before the amount.

A has $500; Bowes $300. If they unite their fortunes, what will they be worth together?

1202. If A had $300 and B owed $500, the firm would be $200 in debt.

1204. Can you give the rule for addition where the quantities have different signs? Which sign does the sum take?

1205. Add:

6. 3x+14, 7x+9, − 23, 4x-5, -2x, and 3x+11.

7. 4a+3x, 2a, -7x-3a, 5x, -9a+x.

8.3b+c, 4a+6b, 5b-9c, -3a, -2a-3b+4c.

9. 1x8, x+4, -4x-3, 7x+16, -5x-10.

10. 4x+23, -8x+21, − 3x+11, −x+5, 9x-3.

SUBTRACTION OF ALGEBRAIC QUANTITIES.

1206. Oral Problems.

1. The thermometer in the morning was 33 degrees, at noon it was 52 degrees. What was the difference in temperature?

2. In December the thermometer was 10 degrees below zero. In July it was 90 degrees above. What was the difference in temperature?

3. Two cities are in the same latitude. One is in 34° east longitude, and the other in 17° west longitude. What is their difference in longitude?

4. What is the difference in longitude between two cities on the equator, one being in 56° west longitude, and the other in 47° west longitude?

5. A boy makes 40% one day and 50¢ the next. How does he stand at the end of the two days?

6. How would he stand if he made 40 one day and lost 50¢ the next day?

7. A man traveled from the town M, 60 miles due north, and then traveled 50 miles due north. How far is he from his starting-point?

8. One day a man goes 50 miles due north; the next day he travels 70 miles due south. How far is he then from his startingpoint?

9. On Monday A is worth $250; on Tuesday he is worth $150. What has he lost in a day?

10. A man has $150 Jan. 1. Feb. 1 he owes $250. What has he lost in a month?

1207. The degrees above zero on a thermometer may be indicated by a plus sign (+); those below, by a minus sign (−).