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Aviation Maintenance Technician Handbook–General

FAA-H-8083-30B Version 2023

Chapter 3

Mathematics in Aviation Maintenance

quotient l d i v i s o r dividend

When the divisor is a decimal, it must be changed to a whole number before dividing. To do this, move the decimal in the divisor to the right until there are no decimal places. At the same time, move the decimal point in the dividend to the right the same number of places. Then divide. The decimal in the quotient is placed directly above the decimal in the dividend.

Example: Divide 0.144 by 0.12

Formula: 1.2 ; 0. 1 2 0.144 = 12. 14.4 ; – 12 ; 24 ; – 24 ; 0

Move the decimal in the divisor (0.12) two places to the right. The result is 12.0. Next, move the decimal in the dividend (0.144) two places to the right. The result is 14.4. Now divide. The result is 1.2.

Formula: Example: The wing area of an airplane is 262.6 square feet ; and its span is 40.4 feet. Find the mean chord of its wing ; using the formula: area ÷ span = mean chord. ; 6.5 ; 4 0. 4 262.6 = 404. 2626.0 ; – 2424 ; 2020 ; – 2020 ; 0

Move the decimal in the divisor (40.4) one place to the right. Next, move the decimal in the dividend (262.6) one place to the right. Then divide. The mean chord length is 6.5 feet.

Rounding Off Decimal Numbers

Occasionally, it is necessary to round off a decimal number to some value that is practical to use. For example, a measurement is calculated to be 29.4948 inches. To use this measurement, we can use the process of “rounding off.” A decimal is “rounded off” by keeping the digits for a certain number of places and discarding the rest. The degree of accuracy desired determines the number of digits to be retained. When the digit immediately to the right of the last retained digit is 5 or greater, round up by 1. When the digit immediately to the right of the last retained digit is less than 5, leave the last retained digit unchanged.

Example: An actuator shaft is 2.1938 inches in diameter. Round to the nearest tenth.

The digit in the tenths column is a 1. The digit to the right of the 1 is a 9. Since 9 is greater than or equal to 5, “round up” the 1 to a 2. Therefore, 2.1938 rounded to the nearest tenth is 2.2.

Example: The outside diameter of a bearing is 3.1648 centimeters. Round to the nearest hundredth.

The digit in the hundredths column is a 6. The digit to the right of the 6 is a 4. Since 4 is less than 5, do not round up the 6. Therefore, 3.1648 to the nearest hundredth is 3.16.

Example: The length of a bushing is 3.7487 feet. Round to the nearest thousandth.

The digit in the thousandths column is an 8. The digit to the right of the 8 is a 7. Since 7 is greater than or equal to 5, “round up” the 8 to a 9. Therefore, 3.7487 to the nearest thousandth is 3.749.

Converting Decimal Numbers to Fractions

To change a decimal number to a fraction, “read” the decimal out loud, and then write it into a fraction just as it is read as shown below.

Example: One oversized rivet has a diameter of 0.52 inches. Convert 0.52 to a fraction. The decimal 0.52 is read as “fifty-two hundredths.”

Formula: 0. 5 2 = 52 “fifty-two” 100 “hundredths”

In the above fraction of 52⁄100, we can divide 4 into each number resulting in a fraction of 13⁄25.