These eight original questions cover binary, truth tables, circuits and memory. Try each before opening the answer.
This set belongs to computing systems and logic. A teacher can go through your working in the one-hour trial class (from RM50), a taught lesson on the Computer Science topic you choose.
Questions
Question 1. Convert the binary number 1101 to decimal.
Answer
The place values are 8, 4, 2, 1. The digits 1, 1, 0, 1 switch on 8, 4 and 1. So 8 + 4 + 1 = 13.
Question 2. Convert the decimal number 37 to binary.
Answer
37 = 32 + 4 + 1. Using place values 32, 16, 8, 4, 2, 1, the digits are 1, 0, 0, 1, 0, 1. So the answer is 100101. Check: 32 + 4 + 1 = 37.
Question 3. Complete the truth table for Q = A AND NOT B when A = 1 and B = 0.
Answer
NOT B = NOT 0 = 1. Then A AND 1 = 1 AND 1 = 1.
Question 4. Write a Boolean expression for this rule: a window alarm sounds if the window is open (W) and the alarm has not been switched off (X).
Answer
Alarm = W AND NOT X. The phrase “not been switched off” means X is 0, so NOT X is the condition.
Question 5. For Q = (D AND S) OR P, find Q when D = 0, S = 1 and P = 1.
Answer
D AND S = 0 AND 1 = 0. Then 0 OR P = 0 OR 1 = 1.
Question 6. A NAND gate gives NOT (A AND B). Find the output when A = 1 and B = 1.
Answer
A AND B = 1. NOT 1 = 0. NAND is 0 only when both inputs are 1.
Question 7. A student says NOT A AND B means the same as NOT (A AND B). Test A = 1, B = 0 in both and decide if the student is right.
Answer
For NOT A AND B: NOT 1 = 0, then 0 AND 0 = 0.
For NOT (A AND B): 1 AND 0 = 0, then NOT 0 = 1.
The outputs differ (0 and 1), so the student is wrong. NOT applies to A alone in the first expression and to the whole bracket in the second.
Question 8. When a computer is switched off, what happens to the contents of RAM, and why does this matter when you are writing a document?
Answer
RAM loses its contents when power is removed, because it is volatile memory. A document that has not been saved to storage is lost. Saving copies the data to storage, which keeps it without power.
If you got these wrong
For questions 1 and 2, revisit place values in binary. For questions 3, 6 and 7, read reading Boolean expressions and truth tables. For questions 4 and 5, use explaining selected logic circuits.
For question 8, see connecting hardware functions to system behaviour.
To repair the weak step with a teacher, see online one-to-one Computer Science tuition.