CHAPTER III. SUBTRACTION. 40. What number must be added to four to make seven? What, then, will be left if 4 is taken from 7? What number must be added to seven to make ten? What, then, will be left if 7 is taken from 10? Copy the following set of numbers, and find what number must be added to each one in the upper row to make the number below the line. Write the required numbers in the empty places above the lines: When you have done this, you will see that, since 7 and 10 make 17, 7 taken from 17 leaves 10; since 6 and 8 make 14, 6 taken from 14 leaves 8; so with each set of numbers. 41. In the following set, under each number in the lower row, write the number that must be added to it to make To 3 we have to add 6 to make 9, so we write 6 under the 3. To 4 we must add 8 to make 12, so we write 8 under the 4. Now in finding what number must be added to 3 to make 9, we have really found what number will be left if 3 is taken from 9. In finding what number must be added to 4 to make 12, we have really found what number will remain if 4 is taken from 12. 42. The operation of finding the number that remains, when a smaller number is taken from a larger, is called subtraction. The result is called the remainder or difference. 43. The number which is to be subtracted is called the subtrahend; and the number which is to be diminished (that is, the number from which the subtraction is made), is called the minuend. 44. A dash is the sign of subtraction, and when placed between two numbers means that the first number is to be diminished by the second. It is called the minus sign. The expression 4-1-3 is read four minus one equals three. 45. Three dots.. are often used for the word therefore. The expression 6+2=8, .. 8-6=2, is read six plus two equals eight, therefore eight minus six equals two. Ex. 21. (Oral.) 1. What number with 5 makes 10? 2. What number taken from 10 leaves 2? 3. 5 is one part of 12, what is the other? 4. What number taken from 12 leaves 11? What number taken from 12 leaves 9? 10. Subtract by threes, from 100 to 1; from 102 to 0; by fours, from 101 to 1; from 102 to 2; from 103 to 3. 11. Subtract by fives, from 102 to 2; from 103 to 3; from 104 to 4; from 100 to 5. 12. Subtract by sixes, from 103 to 1; from 104 to 2; from 105 to 3; from 100 to 4; from 102 to 6. 13. Subtract by sevens, from 106 to 1; from 100 to 2; from 101 to 3; from 102 to 4; from 103 to 5; from 104 to 6; from 105 to 7. 14. Subtract by eights, from 105 to 1; from 106 to 2; from 107 to 3; from 100 to 4; from 101 to 5; from 102 to 6; from 103 to 7; from 104 to 8. 15. Subtract by nines, from 100 to 1; from 101 to 2; from 102 to 3; from 103 to 4; from 104 to 5; from 105 to 6; from 106 to 7. |