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3 questions · 5 marks
Computer systems manipulate bit patterns.
Convert the hexadecimal number D5 to denary.
Award one mark for:
213
Why: 13 × 16 + 5 = 213 (1).
93
Why: Takes the right-hand digit as the 16s, so the value is wrong.
18
Why: Adds the two digits instead of multiplying the first by 16.
Binary, denary and hexadecimal patterns represent numbers.
Convert the denary number -46 to 8-bit binary using two's complement.
Award one mark for each correct nibble in the correct order:
0 marks if the response is not 8-bit binary.
1101 0010
Why: 46 is 00101110; flip the bits (11010001) and add 1: both nibbles are correct (2).
1101 0001
Why: Flips the bits of 46 but doesn't add 1. The first nibble is correct (1); the second is not.
1010 1110
Why: Uses sign and magnitude (a 1 in front of 46) instead of two's complement. Neither nibble is correct.
Computer systems manipulate bit patterns.
Complete the table to show the result of the 8-bit binary addition.
| 128 | 64 | 32 | 16 | 8 | 4 | 2 | 1 |
|---|---|---|---|---|---|---|---|
| 1 | 0 | 1 | 1 | 1 | 0 | 0 | 0 |
| 0 | 0 | 0 | 1 | 1 | 1 | 1 | 1 |
Award one mark for each correct nibble in the correct order:
0 marks if the response is not 8-bit binary.
1101 0111
Why: 184 + 31 = 215, carrying where a column adds to 2: both nibbles are correct (2).
1010 0111
Why: Writes 0 for 1 + 1 but forgets to carry the 1. The second nibble is correct (1); the first is not.
1011 1111
Why: Writes 1 in every column with a 1 and never carries. Neither nibble is correct.
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