These eleven questions cover decomposition, specifications, trace tables, selection with boundary cases and explaining algorithms. Work on paper, write your own trace tables, and open each answer only after you have a result. All code uses Cambridge-style pseudocode.
The module overview is algorithm design. Log wrong answers in the mistake log and use the pseudocode trace trainer to check traces.
Questions
Q1 (easy). A shop program reads the prices of three items and outputs the total after a 10% discount if the total is over RM50, otherwise the total unchanged. List the subproblems in order.
Show answer
- Input the three prices. 2. Add them to get Total. 3. If Total > 50, reduce it by 10%. 4. Output the final amount. Example: 20, 25, 10 gives Total 55, discount 5.5, output 49.5.
Q2 (easy). Write the inputs, outputs and constraints for converting a whole number of minutes into hours and minutes. Give the output for 135.
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Input: Minutes, whole number, 0 or more. Outputs: Hours and Mins, where Mins is from 0 to 59. Hours ← Minutes DIV 60 and Mins ← Minutes MOD 60. For 135: 60 × 2 = 120, so Hours = 2 and Mins = 15. Check: 2 × 60 + 15 = 135.
Q3 (easy). 95 sweets are packed into bags of 8. How many full bags and how many sweets are left?
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8 × 11 = 88, so 95 DIV 8 = 11. 95 − 88 = 7, so 95 MOD 8 = 7. Check: 11 × 8 + 7 = 95.
Q4 (medium). Trace this and give the output.
A ← 2
B ← 1
FOR I ← 1 TO 4
B ← B * A
A ← A + 1
NEXT I
OUTPUT BShow answer
| I | B | A |
|---|---|---|
| start | 1 | 2 |
| 1 | 2 | 3 |
| 2 | 6 | 4 |
| 3 | 24 | 5 |
| 4 | 120 | 6 |
Output 120. Check: 2 × 3 × 4 × 5 = 120.
Q5 (medium). Trace this and give the output.
N ← 27
Steps ← 0
WHILE N > 10 DO
N ← N - 6
Steps ← Steps + 1
ENDWHILE
OUTPUT N, StepsShow answer
27 > 10: N = 21, Steps = 1. 21 > 10: N = 15, Steps = 2. 15 > 10: N = 9, Steps = 3. 9 > 10 is false. Output 9, 3.
Q6 (medium). A discount of 15% applies to orders of RM200 or more. Choose boundary test values (in ringgit and sen) and say what should happen.
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Test 199.99 (no discount), 200.00 (discount, because the rule says 200 or more) and 200.01 (discount). The key test is 200.00, which separates >= from >.
Q7 (medium). The rule is “pass if the mark is 40 or more”, but the code is IF Mark > 40 THEN. Which test finds the fault, and what is the fix?
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Test Mark = 40. The rule expects a pass, but 40 > 40 is false, so the code gives a fail. Fix: IF Mark >= 40 THEN.
Q8 (medium). Write pseudocode for a cinema price: under 5 free, 5 to 17 RM8, 18 and over RM15. Give the output for ages 4, 5, 17 and 18.
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INPUT Age
IF Age < 5 THEN
Price ← 0
ELSE
IF Age < 18 THEN
Price ← 8
ELSE
Price ← 15
ENDIF
ENDIF
OUTPUT PriceOutputs: 4 gives 0, 5 gives 8, 17 gives 8, 18 gives 15.
Q9 (harder). Rewrite this language-specific description as plain steps: “use a for loop with range(1, 6) and the sum function”.
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Set Total to 0. For each whole number from 1 to 5, add it to Total. Output Total. The result is 1 + 2 + 3 + 4 + 5 = 15.
Q10 (harder). Trace the smallest-value algorithm from the lesson on the data 8, 3, 5, 3. Why does it start with the first number?
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Smallest = 8. Next 3 < 8, so Smallest = 3. Then 5 < 3 is false. Then 3 < 3 is false. Output 3. It starts from the first real value, because a fixed start such as 0 could be smaller than every input.
Q11 (harder). Design an algorithm that reads four temperatures and outputs how many are above 30. State the constraints, write the pseudocode and trace 28, 31, 30, 35.
Show answer
Constraints: four temperatures entered as numbers; the output is a whole number from 0 to 4.
Count ← 0
FOR I ← 1 TO 4
INPUT Temp
IF Temp > 30 THEN
Count ← Count + 1
ENDIF
NEXT I
OUTPUT CountTrace: 28 no, 31 yes (Count 1), 30 no (not above 30), 35 yes (Count 2). Output 2.
If you got these wrong
| What went wrong | Go to |
|---|---|
| Subproblems too vague or in the wrong order (Q1, Q9) | Decompose a task |
| Missed DIV or MOD, or no constraints (Q2, Q3) | Inputs, outputs and constraints |
| Trace rows missing or variables out of step (Q4, Q5, Q10) | Trace a sequence |
| Wrong symbol at the edge, or untested boundary (Q6, Q7, Q8) | Selection with boundary cases |
| Explanation tied to a language, or wrong starting value (Q9, Q10, Q11) | Explain an algorithm |
Several slips at once can mean a gap that is easier to fix with someone watching your working. Our online one-to-one Computer Science tuition is built around that kind of tracing and debugging, and the safe Python sandbox lets you check Q11 against a short program.