Edexcel GCSE Computer Science (1CP2) exam questions

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10 questions · 17 marks

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1Multiple choice1 markBinary and Hexadecimal Basics Swap Remove

A computer stores data using binary patterns.

Identify the number of unique states that can be represented by a 4-bit binary pattern.

[1 mark]

Mark scheme

C 16 (1)
The only correct answer is C. The correct answer is 16.
A is not correct because 4 is the number of bits in the pattern, not the number of states it can represent
B is not correct because 8 is the number of states a 3-bit pattern can represent
D is not correct because 32 is the number of states a 5-bit pattern can represent

Example answers and how they were marked

Full marks1/1

C 16

Why: Correct option: a 4-bit pattern can represent 2^4 = 16 unique states (1).

No marks0/1

B 8

Why: Near-miss: 8 is the number of states a 3-bit pattern can represent, not a 4-bit pattern (0).

No marks0/1

A 4

Why: Misconception: 4 is the number of bits in the pattern, not the number of unique states it can represent (0).

2Convert1 markBinary to Denary Conversion Swap Remove

Computers manipulate binary patterns.

Convert the binary pattern 1110 0000 to denary.

[1 mark]

Mark scheme

Award one mark for:

224 (1)

Example answers and how they were marked

Full marks1/1

224

Why: Correct: 128 + 64 + 32 = 224 (1).

No marks0/1

Why: Reads the place values from the wrong end (the left-hand bit as 1), so the value is wrong.

No marks0/1

Why: Counts the 1s instead of adding their place values.

3Convert1 markDenary to Hexadecimal Conversion Swap Remove

Computer systems manipulate bit patterns.

Convert the hexadecimal number 8F to denary.

[1 mark]

Mark scheme

Award one mark for:

143 (1)

Example answers and how they were marked

Full marks1/1

143

Why: 8 × 16 + 15 = 143 (1).

No marks0/1

248

Why: Takes the right-hand digit as the 16s, so the value is wrong.

No marks0/1

Why: Adds the two digits instead of multiplying the first by 16.

4Short recall2 marksBinary and Hexadecimal Basics Swap Remove

Hexadecimal is often used by programmers.

Give two reasons why programmers use hexadecimal.

[2 marks]

Mark scheme

Award one mark for any of the following up to a maximum of two marks:

Hexadecimal is shorter than binary/uses fewer digits (1)
It is quicker/easier to read/write (than binary) (1)
It is easier to remember (than binary) (1)
Fewer digits mean less chance of error when reading or typing (1)
It is easy to convert between hexadecimal and binary (1)

Do not accept 'easier'/'better' on its own without saying what is easier/better, e.g. easier to read/write.

For the less chance of error point, accept reading or typing on its own.

Do not award the less chance of error point for a response that only says hexadecimal is shorter/uses fewer digits.

Do not award two marks for the same reason repeated in different words; a second, different reason is needed for the second mark.

Do not accept hexadecimal takes less storage space/uses less memory than binary.

Example answers and how they were marked

Full marks2/2

Hexadecimal is shorter than binary, so it is quicker to read and write. Having fewer digits also means there is less chance of making an error when typing a value.

Why: First sentence gives two creditworthy reasons: hexadecimal is shorter/uses fewer digits (1) and it is quicker to read/write (1). The second sentence gives a further valid reason but is beyond the two-mark cap.

Some marks1/2

Hexadecimal is shorter than binary.

Why: Gives one creditworthy reason: hexadecimal is shorter/uses fewer digits than binary (1). No second, different reason is given.

No marks0/2

Hexadecimal takes less storage space than binary.

Why: This is a misconception; hexadecimal does not take less storage space than binary, and the mark scheme does not accept it.

5Describe2 marksBinary and Hexadecimal Basics Swap Remove

An electronic lock stores each of its codes as a 4-bit binary pattern.

Describe how the number of different codes that can be stored can be calculated.

[2 marks]

Mark scheme

Award up to two marks for a linked description such as:

Each bit has two possible values/states (0 or 1) (1) so the number of codes is 2 × 2 × 2 × 2 = 16 (1)
The number of bits is used as the power of 2 (1) so for 4 bits the number of codes is 2^4 = 16 (1)
Each extra bit doubles the number of possible codes (1) so 4 bits give 2 × 2 × 2 × 2 = 16 codes (1)

Do not accept 15 (or 2^4 − 1): this is the largest value a 4-bit pattern can hold, not the number of different codes.

Do not award a response that only states 16 or '2^4 = 16' without a linked description.

Do not award '2 to the power of 4' on its own without a linked description, such as two values per bit or the number of bits used as the power of 2.

Example answers and how they were marked

Full marks2/2

Each bit can be either 0 or 1, so there are two possibilities for every bit. For a 4-bit code this is 2 × 2 × 2 × 2 = 16 different codes.

Why: Two possible values for each bit (1) linked to multiplying for 4 bits to get 16 (1).

Some marks1/2

Each bit has two possible values.

Why: Gives the first point (1) but does not link it to calculating the number of codes.

No marks0/2

The largest number a 4-bit pattern can hold is 15, so 15 different codes can be stored.

Why: Classic misconception: 15 is the largest value a 4-bit pattern can hold, not the number of different codes; the mark scheme says not to accept 15.

6Convert2 marksBinary to Hexadecimal Conversion Swap Remove

Computer systems manipulate bit patterns.

Convert the binary pattern 1000 1010 to hexadecimal.

[2 marks]

Mark scheme

Award one mark for each correct digit in the correct position:

8 (1)
A (1)

Answer: 8A

Example answers and how they were marked

Full marks2/2

Why: Each nibble is one hexadecimal digit: 1000 = 8, 1010 = A: both digits are correct (2).

Some marks1/2

810

Why: One digit is correct (1), but a digit over 9 is written in denary instead of as a letter.

No marks0/2

Why: The digits are the wrong way round, so neither is in the correct position.

7Convert2 marksDenary to Hexadecimal Conversion Swap Remove

Computer systems manipulate bit patterns.

Convert the denary number 244 to hexadecimal.

[2 marks]

Mark scheme

Award one mark for each correct digit in the correct position:

F (1)
4 (1)

Answer: F4

Example answers and how they were marked

Full marks2/2

Why: 244 ÷ 16 = 15 remainder 4, so the digits are F and 4: both digits are correct (2).

Some marks1/2

154

Why: One digit is correct (1), but a digit over 9 is written in denary instead of as a letter.

No marks0/2

Why: The digits are the wrong way round, so neither is in the correct position.

8Convert2 marksDenary to Negative Binary Conversion Swap Remove

Computer systems manipulate bit patterns.

Convert the 8-bit binary two's complement pattern 1100 1011 to denary.

[2 marks]

Mark scheme

Award one mark for each of:

− (negative sign) (1)
53 (1)

The correct answer is −53

Example answers and how they were marked

Full marks2/2

−53

Why: The left-hand bit is worth −128: −128 + 75 = -53. Sign (1) and value (1).

Some marks1/2

Why: The value is right (1) but the minus sign is missing.

No marks0/2

203

Why: Reads it as an unsigned number, so neither the sign nor the value is right.

9Calculate2 marksAdding Binary Numbers Swap Remove

Binary patterns can represent numbers.

Complete the table to show the result of the 8-bit binary addition.

[2 marks]

128	64	32	16	8	4	2	1
1	0	0	1	0	1	1	0
0	1	0	1	1	1	0	0

Mark scheme

Award one mark for each correct nibble in the correct order:

1111 (1)
0010 (1)

0 marks if the response is not 8-bit binary.

Example answers and how they were marked

Full marks2/2

1111 0010

Why: 150 + 92 = 242, carrying where a column adds to 2: both nibbles are correct (2).

Some marks1/2

1111 0011

Why: A slip in the last bit. The first nibble is correct (1); the second is not.

No marks0/2

1101 1110

Why: Writes 1 in every column with a 1 and never carries. Neither nibble is correct.

10Calculate2 marksBinary Shifts Swap Remove

Binary, denary and hexadecimal patterns represent numbers.

Complete the table with the result of applying the shift to the binary pattern.

[2 marks]

Binary pattern	Shift	8-bit binary result
1010 1100	Arithmetic shift right by 1

Mark scheme

Award one mark for each correct nibble in the correct order:

1101 (1)
0110 (1)

0 marks if the response is not 8-bit binary.

Example answers and how they were marked

Full marks2/2

1101 0110

Why: Every bit moves 1 place right, with copies of the sign bit (1) in from the left: both nibbles are correct (2).

Some marks1/2

0101 0110

Why: Fills the gap on the left with 0s, as a logical shift would, instead of copying the sign bit. The second nibble is correct (1); the first is not.

No marks0/2

0101 1000

Why: Shifts the bits the wrong way. Neither nibble is correct.

Edexcel GCSE Computer Science (1CP2) Exam Questions

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Questions by topic

2.1 Binary

2.2 Data representation

2.3 Data storage and compression

3.1 Hardware

3.2 Software

3.3 Programming languages

4.1 Networks

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