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Computer fundamentals and programming: board exam questions with solutions

On the ECE exam under General Engineering and Applied Sciences (GEAS) and the REE exam under Engineering Sciences and Allied Subjects (ESAS). Try each question before you open its solution, then practise with fresh numbers below: 2 computed question types on this topic.

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Questions

1. Convert 10110110₂ to hexadecimal.

  1. 6B
  2. D6
  3. B6
  4. B5
Show the answer and solution

Answer: C. B6

Group the bits in fours: 1011 = B and 0110 = 6, giving B6₁₆.

2. How many bytes are in 1 KiB (kibibyte)?

  1. 1000
  2. 512
  3. 1024
  4. 8192
Show the answer and solution

Answer: C. 1024

The binary prefix kibi means 2¹⁰ = 1024. kB (kilo) is 1000 bytes.

3. What is the 8-bit two's-complement representation of −45?

  1. 11010010
  2. 11010011
  3. 10101101
  4. 00101101
Show the answer and solution

Answer: B. 11010011

45 = 00101101. Inverting gives 11010010 (the one's complement), and adding 1 gives 11010011.

4. Convert 255₁₀ to octal.

  1. 777₈
  2. 255₈
  3. FF₈
  4. 377₈
Show the answer and solution

Answer: D. 377₈

255 = 3×64 + 7×8 + 7, so it is 377₈. (255 = 11 111 111₂, grouped in threes.)

5. Simplify the Boolean expression A + A·B.

  1. B
  2. A
  3. A·B
  4. A + B
Show the answer and solution

Answer: B. A

By absorption, A + AB = A(1 + B) = A·1 = A.

6. An IPv4 subnet uses the prefix /26. How many usable host addresses does it have?

  1. 62
  2. 64
  3. 30
  4. 126
Show the answer and solution

Answer: A. 62

32 − 26 = 6 host bits gives 2⁶ = 64 addresses. Subtracting the network and broadcast addresses leaves 62 usable hosts.

7. Which type of memory loses its contents when power is removed?

  1. DRAM
  2. Flash memory
  3. EEPROM
  4. Mask ROM
Show the answer and solution

Answer: A. DRAM

DRAM stores bits as charge on capacitors that must be refreshed, so it is volatile. Flash, EEPROM and ROM are non-volatile.

8. Ignoring protocol overhead, how long does a 50 MB file (1 MB = 10⁶ bytes) take to transfer over a 20 Mbps link?

  1. 2.5 s
  2. 2.4 s
  3. 160 s
  4. 20 s
Show the answer and solution

Answer: D. 20 s

50 MB = 400×10⁶ bits, and 400×10⁶/20×10⁶ = 20 s. Forgetting the factor of 8 bits per byte gives 2.5 s.

Worked examples with computed numbers

These numbers are fixed on this page; in practice they change every time.

9. Convert 9A04₁₆ to decimal.

  1. 39428
  2. 9
  3. 39684
  4. 39412
Show the answer and solution

Answer: A. 39428

9A04₁₆ = 9×16^3 + 10×16^2 + 0×16^1 + 4×16^0 = 39428.

10. What is −67 in 8-bit two's complement?

  1. 01000011
  2. 10111101
  3. 11000011
  4. 10111100
Show the answer and solution

Answer: B. 10111101

Invert 01000011 and add 1: 10111101.

Other topics in the same subjects

Physics: mechanics · Physics: waves, electricity and magnetism · General chemistry · Thermodynamics · Engineering materials · Engineering economics · Engineering management · RA 9292 and ethics (electronics) · Fluid mechanics · Strength of materials · RA 7920 and ethics (electrical) · PEC Part 1: general requirements

An independent, free reviewer: not affiliated with the PRC or the Boards. Subject weights and passing rules are from the PRC examination programs and the laws (RA 9292, RA 7920); check the current PRC program before you file. Code questions follow the Philippine Electrical Code 2017 Part 1; check them against your own copy of the Code.