27. If 76 acres of land are bought at $ 740 an acre, what is the total cost ? 28. A dealer sells 182 sets of harness at. $ 26 a set. What does he receive ? 29. If in walking a mile a man averages 2112 steps, how many steps will he take in walking 27 miles ? 30. 1972 pickets are required to fence one side of a square field. How many pickets will be required to fence 19 fields of the same size and shape ? 31. In a freight train are 32 cars, each containing 82 barrels of flour, each barrel weighing 196 pounds. How many pounds of flour in the trainload ? 32. An oil well driller charged 35 cents per foot for drilling and 75 cents per foot for the tubing. If the well was drilled 1220 feet and tubed 720 feet, what was the cost ? Short Methods There are many combinations of numbers which can be multiplied by certain short methods and the student should always be on the lookout for number combinations which will lessen labor in computation. Multiplication by 25. Rule. — To multiply by 25, add two ciphers and divide by 4. EXAMPLE. Multiply 28 by 25. 28 x 25 = 28 x 100 = 4= 700. ORAL DRILL By this method find the results of the following indicated multiplications: 1. 2. 3. 4. 5. 8 12 16 20 24 25 25 25 25 26. How much will 42 army rifles cost at $ 25 apiece ? 27. Find the cost of 3 dozen overcoats at $ 25 each. 28. What will be the bill for 76 hours of work at 25 cents per hour ? 29. What will it cost to fill an 18-gallon gasoline tank at 25 cents per gallon ? 30. Find the cost of 8 cans of salmon eggs at 25 cents per can. 31. What will 12 pairs of men's hose cost at 25 cents a pair? 32. What will be the cost of 22 saucepans at 25 cents apiece ? 33. Find the cost of 24 cans of sardines at 25 cents a can. 34. How much will 11 bottles of sewing machine oil cost at 25 cents a bottle ? 35. Find the cost of three and a half dozen electric light bulbs at 25 cents each. Exercise By the same method find the results of the following indicated multiplications : Multiplication by 125. Rule. - To multiply by 125, add three ciphers and divide by 8. EXAMPLE. Multiply 72 by 125. 72 X 125 = 72 x 1000 + 8 = 9000. Exercise By this method find the results of the following indicated multiplications: 26. What will 500 copies of Strong's “ Tractor Farming" cost at $ 1.25 per copy? 27. What will 350 copies of Walker's “The Uphill Road” cost at $ 1.25 per copy ? 28. Find the cost of 30 boxes of cartridges at $ 1.25 a box. 29. What will 12 baseballs cost at a dollar and a quarter apiece? 30. What will 50 pairs of tennis shoes cost at $ 1.25 a pair? 31. Find the cost of 16 phonograph records at $ 1.25 each. 32. Find the cost of 6 dozen bandanna handkerchiefs at $ 1.25 a dozen. 33. What will one dozen baseball mitts cost at $ 2.50 each? 34. What will 125 sheep cost at $ 12.50 per sheep? To Multiply Such Numbers as 63 and 67. When two numbers are such that the left-hand digits are the same and the sum of the right-hand digits is ten, multiplication is readily effected by the following rule. Rule. Increase the left-hand digit of one of the numbers by 1 and multiply it by the left-hand digit of the other number; this will give the first figure or figures in the answer. Multiply the two right-hand digits together; this will give the other figures in the answer. |