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Rule for rounding up a decimal

Aviation Mechanic General (AMG) practice question 7 of 25 on Mathematics. ACS element AM.I.H.K9 · difficulty: recall. Want to answer it in a timed quiz? Use the Aviation Mechanic General (AMG) practice mode.

Question bank updated 2026-09-22

QUESTIONWhen rounding off a decimal number, the last retained digit is increased by 1 when the digit immediately to its right is

  1. A5 or greater
  2. Bgreater than 5
  3. C4 or greater
Show the answer and explanation

Correct answer: A. 5 or greater

  • A — correct The handbook rule: when the digit to the right of the last retained digit is 5 or greater, round up by 1; when it is less than 5, leave the retained digit unchanged.
  • B — incorrect A 5 itself also causes rounding up; the threshold is 5 or greater, not strictly greater than 5.
  • C — incorrect A 4 is less than 5, so the retained digit is left unchanged.

BACKGROUND

It is sometimes necessary to round off a decimal number to a value that is practical to use, such as a measurement calculated to be 29.4948 inches. Rounding keeps the digits for a certain number of places and discards the rest; the degree of accuracy desired determines how many digits are retained. When the digit immediately to the right of the last retained digit is 5 or greater, round up by 1. When that digit is less than 5, leave the last retained digit unchanged. For example, 2.1938 rounded to the nearest tenth is 2.2.

STUDY TIP

Look at only the single digit to the right of the place you are rounding to; 5 through 9 round up, 0 through 4 do not.

KEY POINTS

  • Digit to the right is 5 or greater: round up by 1.
  • Digit to the right is less than 5: leave unchanged.
  • 2.1938 to the nearest tenth = 2.2.

SOURCES

  • FAA-H-8083-30B ch03 "Rounding Off Decimal Numbers"
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SkyDrill is not affiliated with the FAA. This is an original practice item based on FAA-H-8083-30B Aviation Maintenance Technician Handbook – General, 14 CFR part 43 and part 65. Regulations and handbooks are revised; confirm details against the current edition.