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MATHEMATICS FOR AIR CREW TRAINEES         11-12

(7) A tank is five-sixths full of gas. If one-eigth of this is drawn off, what part of the whole tank is drawn off? What part remains in the tank?

(8) The circumference of a circle is about 3 1/7 times the diameter. Find the circumference of a circle if the diameter is 14 feet; if 28 feet; if 1/22 foot. 44ft; 88ft; 1/7 ft  Answers.

(9) If a motor makes 2,100 rpm, how many revolutions does it make in 3/4 hour? In 3 10/21 days?

(10) An alloy used for bearings in machinery is 24/29 copper, 4/29 tin, and 1/29 zinc. How many pounds of each in 246 pounds of the alloy?
286.34 lb copper; 47.72 lb tin; 11.93 lb zinc  Answers.

12. Division of fractions.-a. To divide one fraction by another, first invert the divisor and then multiply as in paragraph 11.

Example: Divide 8/9 by 15/17.
Solution:
Figure 10.

b. To divide mixed numbers, first change to a fractional form, then divide as in a above. 

Example: Divide 7 2/3 by 8 3/4
Solution: 7 2/3 / 8 3/4 = 23/3 / 35/4 = 23x4/3X25 = 92/105 Answer.

c. Exercises
(1)5/7 / 10 = ?
(2)1/3 / 4/3 = ?  1/4 Answer.
(3)27 3/5 / 9 = ?
(4)5 1/2 / 2 3/4 = ? 2 Answer.
(5) In the blueprint of a house 1/4 inch in the print represents 1 foot in the actual house. Find the dimensions of the rooms that measure as follows: 2 1/2 by 2 1/2 inches, 4 1/2 by 4 5/8 inches, 5 3/8 by 6 inches, 3 1/16 and 4 10/32 inches, respectively, on the blueprint.

(6) Two places, A and B, are 24 miles apart on a river that flows 3 miles an hour. A man can row 5 miles an hour in still water. He goes from A to B and back. Find the time for the journey. 
Hint: Man's speed down river is 8 mph.    15 hr Answer.

(7) A car is going 11.25 miles per hour. How long will it take this car to go 486 3/4 miles?
 
(8) A layer of No.8 wire, 0.162 inch in diameter, is wound on a pipe 24 3/8 inches long. How many turns of wire are wound on the pipe?       150.46 turns Answer.

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