O-LevelComputer ScienceAlgorithm design and problem-solving2210/22 · Oct/Nov 2019 · Q37 Marks

(a) The flowchart checks the lengths of a batch of 10 ropes. For the batch to be accepted 90% of the lengths need to be between 24.9 and 25.1 metres. [Figure 3.1]

(a)Complete the trace table for the input data: 24.88, 25.01, 24.98, 25.00, 25.05, 24.99, 24.97, 25.04, 25.19, 25.07 Reject | Count | Length | OUTPUT ---|---|---|---[4]
(b)(i)It has been decided to only reject batches of rope that contain ropes that are too short. State the change required to the algorithm.[1]
(b)(ii)Explain how the algorithm to reject batches could be improved to make it more effective.[2]

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2019). The mark or mark type is shown in brackets.

[4] One mark for each correct column max. 4
Reject | Count | Length | OUTPUT
---|---|---|---
0 | 0 | |
0 | 1 | 24.88 |
1 | 2 | 25.01 |
1 | 3 | 24.98 |
1 | 4 | 25.00 |
1 | 5 | 25.05 |
1 | 6 | 24.99 |
1 | 7 | 24.97 |
1 | 8 | 25.04 |
1 | 9 | 25.19 |
2 | 10 | 25.07 | Batch rejected
[1] ∞ Remove Length < 25.1 AND
[2] Two from:
∞ Check the reject counter after each incrementation/remove reject check after counter = 10
∞ as soon as Reject = 2 / >1 ...
∞ reject batch and end

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