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The decimal number system uses the characters 0, 1, 2, ..., 9 and the octal number system uses the characters 0, 1, 2, ..., 7. For example, the decimal number 12 (= 1 x 8^1 + 4 x 8^0) is expressed as 14 in the octal number system. The decimal number 108 in the octal number system is: A. 104 B. 128 C. 150 D. 154

GATE 2024 · General Aptitude · Number System · medium

Answer: (154)_8 = 108_10. Answer D.

  1. Divide 108 by 8: 108 = 13 * 8 + 4. So the units digit (8^0 position) is 4. Carry forward quotient 13.
  2. Divide 13 by 8: 13 = 1 * 8 + 5. The 8^1 digit is 5. Carry forward quotient 1.
  3. Divide 1 by 8: 1 = 0 * 8 + 1. The 8^2 digit is 1. Quotient is 0, so we stop.
  4. Verify by expansion: (154)_8 = 1*64 + 5*8 + 4 = 64 + 40 + 4 = 108. Confirmed.