1. Unit 8
Tracing Algorithms

12. Unit 8
Tracing Algorithms

13. Most exam questions ask you to TRACE an algorithm.
It is ESSENTIAL that you follow the correct procedure.

19. Exam Technique
Ensure each line is recorded down the side in the order they appear
Ensure each letter is recorded along the top in the order they appear
Instructions such as ‘If’ ‘then go to’ do not need to be recorded
If the algorithm says print, add this to the top headings and print the value
You do not need to add a separate line for ‘end’

21. P R T I A M
Print
Line 10
400
Line 20 5 3
Line 30 60
Line 40
460
Line 50
Line 60
12.8
Line 70
12.8

22. P R T A K I M
Print
Line 10
400
Line 20 5 3
Line 30
400
Line 40
Line 50
Line 60 1
Line 70 20
Line 80
420
Line 60 2
Line 70 21
Line 80
441
Line 60 3
Line 70
22.05
463.05
Line 80
12.9
Line 100
12.9
Line 110

24. A B
C D
Print
Line 10
2 3
Line 20
0 0
Line 30 2
Line 40 3 4
Line 70
Line 90 6
Line 70 6
Line 110 6

25. A B
C D
Print
Line 10
6 8
Line 20
0 0
Line 30 6
Line 40 8 12
Line 70
Line 90 16
Line 70 18
Line 90 24
Line 70 24
Line 110 24
The algorithm defines the LOWEST COMMON MULTIPLE of two integers
When A = 200 and B = 300, then C will be
600

27. Model Answer 6ai)
Line
A B C D K N X Y 10 20 1 30 40 1 50 80 1
100 2 40 2 50 80 2
100 3 40 3 50 80 3

28. Model Answer 6aii)
Line
A B C D K N X Y 10 20 1 30 40 1 50 80 1
100 2 40 2 50 6
100 3 40 3 50 4
100 4 40 4

29. Model Answer 6aii)
Line
A B C D K N X Y 80 2
100 5 40 5 50 80 3
Explain where and why this algorithm would fail if A = 0
At Line 90
As N would never = 3

30. Ques 8 X
A B
Print
Line 10
20 8
Line 20
Line 60 10 16
Line 70
Line 60 5
Line 70 32
Line 40 32
Line 60 2 64
Line 70 1
Line 60
128
Line 70
Line 40
160
Line 90
160
The algorithm defines the MULTIPLICATION of A and B
A CONTINUOUS
LOOP
If Line 50 read If A = 1, then go to Line 80 it would create