Ex. 34. (Oral.) 1. Of what number are 2 and 4 the factors? 3 and 3? 5 and 3? 2 and 5? 3 and 6? 2. What are the factors of 14? of 9? of 8? of 18? of 6? of 21? of 10? 3. 4 is one factor of 8; 3 is one factor of 12; 9 is one factor of 18; what is the other? 4. 3 times what number make 15? 6 times what number make 18? 5 times what number make 25? 5. 8 times what number make 24? 6 times what number make 24? 6 times what number make 12? 42? 30? 18? 6. 7 times what number make 21? 63? 35? 49? 56? 14? 7. 8 times what number make 32? 64? 16? 40? 24? 56? 8. 9 times what number make 27? 72? 45? 63? 36? 18? to 56. When the multiplicand consists of two or more digits, and the multiplier is a single digit, it is necessary multiply each digit of the multiplicand by the multiplier. Thus, the product of 6× 4587 is the sum of six numbers, each the same as the multiplicand. 4587 4587 4587 or 6 4587 4587 27522 The sum of the six 7's is 6 times 7 = 42, and we write the 2 units in the column of units, and reserve the 4 tens to be added to the product of the tens; then 6 times 8 tens 48 tens, which, with the 4 tens, make 52 tens, or 5 hundreds and 2 tens, and we write the 2 tens in the column of tens; then 6 times 5 hundreds 30 hundreds, which, with the 5 hundreds, make 35 hundreds, or 3 thousands and 5 hundreds, and we write the 5 hundreds in the column of hundreds: then 6 times 4 thousands = 24 thousands, which, 4587 with the 3 thousands, make 27 thousands, and we write 27 to the left of the 5 hundreds. 57. When the multiplier is 10, 100, 1000, etc., the product is obtained by simply annexing as many zeros to the multiplicand as are found in the multiplier. Thus : Likewise, when the multiplier is any one of the nine significant* digits followed by zeros, the product is obtained by multiplying the multiplicand by the significant digit and annexing to the result as many zeros as are found in the multiplier. Thus, if the multiplicand is 4587, and the multiplier is 600, we multiply by 6 and obtain 27,522, and annex to this result 2 zeros, and have for the required product 2,752,200: 4587 * The digits 1, 2, 3, 4, 5, 6, 7, 8, 9 are called significant digits. |