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