6. Periods. For convenience in reading and writing numbers the figures of a number are divided into periods of three places each. The first three places make the first or units period, the second three places make the second or thousands period, etc. The periods are separated from each other by commas. EXERCISES ON THE TABLE. 1. Name the periods in order from units to quadrillions. 2. Name the places in order from units to quadrillions. Name the following periods: 16. 17. 18. 19. 10,000 60,214 100,000 625,324 20,000 70,809 200,000 704,897 30,000 80,029 300,000 820,614 26. 1 million 320 thousand 412. Copy, point off, and read- 27. 126 million 216 thousand 812. 36. 70010003. WRITTEN EXERCISES. 15.-1. What is the sum of 65 and 87? PROCESS. 65 87 152, Ans. For convenience we write the numbers with units under units and tens under tens, and begin at the right to add. The sum of 7 units and 5 units is 12 units, which equal 1 ten and 2 units; we write the 2 units under the column of units, and add the 1 ten to the column of tens. The sum of 1 ten, 8 tens, and 6 tens is 15 tens, which equal 1 hundred and 5 tens; we write the 5 tens under the column of tens, and place the 1 hundred on the left in the place of hundreds. 2. What is the sum of 455, 789, and 347? PROCESS. In practice we name results only in adding; thus, we say 7, 16, 21; write 1 and carry 2. 455 789 347 1591, Ans. Then 1, 4, 11, 15; write 15. Then 2, 6, 14, 19; write 9 and carry 1. PROOF.-Begin at the top and add downward; if the two results agree, the work is probably correct. 387 205 562 785 3.72 4.67 8.71 4.44 |