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27-29            ARMY AIR FORCES

(7) An airplane flying a course against the wind covers 160 miles in 1 hour. At a later time the airplane flies the return trip with the wind, with a ground speed of 200 miles per hour. If the round trip took 5 hours, what was the round-trip distance?

(8) Solve for x:    3x/2 - 4/3 (x-5) - 1/6(5x-12)=0       x=13 Answer.

(9) Evaluate when x=-1, y=4, z=2:    xy•x^2 + 4(yz+x) - x^3 + yz^2

(10) One observation airplane can map a certain region in 1 hour. A second airplane can map the region in 1 1/2 hours. How long will it take the two to do it together.                        

3/5 hr Answer.

(11) A ferry pilot travels 800 miles by airplane and 100 miles by train in 4 hours 40 minutes. Then, at the same speeds as before, he flies 700 miles in another airplane and 150 miles by train in a total of 5 hours and 20 minutes. What were the speeds of the airplanes and trains?

SECTION IV

SCALES

                                        Paragraph
Scope ----------------------------------- 28
Models ---------------------------------- 29
Maps ------------------------------------ 30
Miscellaneous exercises ----------------- 31

28. Scope.—The word "scale" is used in this section as in "scale model," the "scale of a map," the "scale of a drawing," and so on. The practical use of scales in connection with maps, drawings, and silhouettes is illustrated by examples and exercises.

29. Models.—a. A true scale model of an airplane, for example, is a model which has been constructed so that the ratio of the length of any part of the model to the actual length of the same part of the airplane is the same for all parts. Thus, if the wing span on the model is 5 inches, and the wing span of the actual airplane is 55 feet, then 1 inch anywhere on the model represents 11 feet or 132 inches. Then this is the scale of the model: 1 to 132, or 1/132. When a scale is stated simply as 1 to 132 it means that 1 unit of any kind of the model represents 132 of the same kind of units on the airplane. In other words, the model is 1/132 the size of the airplane. 

b. Example: The U.S. Government is encouraging youths to build scale models of various aircraft. The scale to be used is the same for all aircraft: 1 to 72. The wing span of the German Heinkel bomber 

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