We see that when we multiply a number by 1000 we annex three O's to it. 3. Multiply each of the following numbers by 1000 and write only the products: 16 45 92 81 19 35 58 62 112 416 300 450 217 430 255 800 21. Multipliers Ending in O's When we multiply by a number ending in O's, it is convenient to write the multiplier with the O's to the right, as shown in the models below. We multiply by the whole number and annex the O's. 1. Copy and multiply in the most convenient way. Use your pencil only when necessary. 2. Find the number of bushels of corn grown on: 40 acres, yielding 80 bushels to the acre. 30 acres, yielding 100 bushels to the acre. 100 acres, yielding 110 bushels to the acre. 150 acres, yielding 100 bushels to the acre. 3. Tell how much a farmer should receive for: 800 bushels of corn at $1.00 a bushel. 900 bushels of oats at $1.05 a bushel. 4. Find the weight of 64 bales of cotton, each weighing 500 pounds. 22. Two-Figure Multipliers Write the 4 directly under the 2 you are multiplying by. 2X9-18, 18+1=19. Write 9. Remember the 1. 2X1=2, 2+1=3. Write 3. Step 3. Add the partial products. When multiplying by a number containing more than one figure, write the right-hand figure of each partial product under the figure by which you are multiplying. 1. William's teacher told him to multiply 249 by 32. When William finished, he said his answer was 8068. Was he correct? 2. Another time William multiplied 163 by 48. If his work was correct, what answer did he get? 3. John was absent when the class began to multiply by two-figure numbers. If John were in your class, could you explain to him how to multiply 634 by 52? Perhaps your teacher will let you go to the board and show how you would do it. 4. Mary and William worked the same examples to bring to class. Below are some of the examples for which they got different answers. Tell who was right in each case: Mary's Answers William's Answers 23. Making Problems in Class The teacher asked her pupils to bring problems to class. Here are some of the problems that were brought. See how many of them you can work. 1. William's problem: There are 11 boys on my football team. How much will it cost us to buy uniforms for the whole team at $9.75 each? Be sure to point off two places in the product for cents. 2. Mary's problem: My aunt who lives on a farm sold 17 dozen chickens at $13.25 a dozen. How much did she receive for the chickens? 3. John's problem: My father bought 23 acres of land at $47.35 an acre. How much did the land cost him? 4. Susan's problem: Last month our baker used 39 barrels of flour, each costing him $6.86. What was the total cost of the flour he used? 5. Henry's problem: There are 16 boys in this class. How much money would it take to buy each a suit of clothes costing $13.50? 6. Bring to class two problems that are similar to those given in this exercise. Kate earned $7.50 by helping her mother. She spent $3.50 for a tennis racket and $1.60 for balls. much money did she have left? How The problem tells us how much money Kate had and that she spent some of it. It asks us to find out how much money she had left. There are two steps in solving this problem: To find how much Kate spent. To find how much she had left. $3.50 1.60 $5.10 $7.50 5.10 $2.40 To find the amount Kate had spent, we add $3.50 and $1.60. The sum is $5.10. To find the amount she had left, we subtract $5.10 from $7.50. The remainder is $2.40. In solving problems that seem difficult, ask yourself these questions: What does the problem tell me? What operations must I use? Before working problems, it is well to estimate the answers. Solve the following problems in the way the problem at the beginning of this exercise was solved: 1. A man had saved $3280. After buying three lots at $965 each, how much money did he have left? 2. A boy earned $15.75 in one month. He spent of it and put the remainder in the bank. How much money did he have left? 3. Ruth's mother gives her an allowance of 25¢ a week. At the end of 12 weeks she puts of this money in the bank. How much does she put in the bank? 4. Mary's mother bought 4 yards of 75-cent cloth for her dress and dozen buttons at 40¢ a dozen. How much did the materials cost? |