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MATHEMATICS FOR AIR CREW TRAINEES      15-17

15. Addition of positive and negative numbers.--To add two numbers which have the same signs, add the numbers and prefix the common (or same) sign. If the numbers to be added have unlike signs, find the difference and use the sign of the larger number.
a. Example: (+6)+(-3)=?
   Solution: Since the signs are different, subtract the numbers to obtain a remainder of 3. Since the sign of the larger number is positive, the sign of the remainder is also positive: 6+(-3)=3                 Answer.
b. Example: (-3)+(+2)=?
   Solution: Referring to figure 22, begin at -3 and count 2 units in a positive direction. The result is 1 space to the left of zero. Therefore (-3)+(+2)=-1.
This problem may also be done by using the rule stated in the preceding paragraph. Since the signs are unlike, subtract 2 from 3 and prefix the remainder by a minus sign since the larger number is negative.              
                                                    (-3)+(+2)=-1  Answer.

16. Subtraction of positive and negative numbers.--a. To subtract two numbers (positive or negative), change the sign of the number being subtracted and add the numbers as in addition (par. 15). 
   Example: (-3)-(-4)=?
   Solution: Changing the sign of the number being subtracted, the problem then becomes--
                        (-3)+(+4)=+1                               Answer.

b. Exercises.
     (1) (-6)+(+6)=?
     (2) (+2)+(+12)=+14                                            Answer.
     (3) (-62)+(-18)=?
     (4) (+17)-(+15)=+2                                            Answer.
     (5) (+32)-(-64)=?
     (6) (-18)-(-64)=+46                                           Answer.
     (7) (-17)-(-15)=?
     (8) (-17.3)+(35.4)=+18.1                                      Answer.
     (9) (-17.36)-(35.4)=?
     (10) (-201.03)-(-10.4)=-190.63                                Answer.
     (11) -18+.4=?
     (12) 20-17.4+9=11.6                                           Answer.
     (13) -37.3+19.4+17.8=?
     (14) (-175.03)+19=-156.03                                     Answer.
17. Multiplication and division of positive and negative numbers.--a. If the two numbers to be multiplied have the same signs, then the product is positive. If the two numbers to be multiplied have opposite signs, then the product is negative.

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