D1 June 2012 Q6
6.
Figure 5 is the activity network relating to a development project. The activities are represented by the arcs. The number in brackets on each arc gives the time, in days, to complete the activity. Each activity requires one worker. The project is to be completed in the shortest possible time.
| Scheme | Marks | ||||||||||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| B2, 1, 0 | ||||||||||||||||||||||||||||||
| (2) |
Notes
a1B1 Any 3 rows completed correctly
a1B2 All five rows completed correctly
| Scheme | Marks |
|---|---|
 | 1M1 1A1 2M1 2A1 |
| (4) |
Notes
b1M1 All top boxes complete, values generally increasing left to right, condone one rogue
b1A1 CAO
b2M1 All bottom boxes complete, values generally decreasing R to L, condone one rogue. Condone missing 0 or 28 for the M only.
b2A1 CAO
| Scheme | Marks |
|---|---|
| Total float on E = 21 – 5 – 3 = 13 | M1 A1 |
| (2) |
Notes
c1M1 Correct calculation seen all three numbers correct (ft). Float \(\geqslant 0\).
c1A1 CAO
| Scheme | Marks |
|---|---|
| \(\dfrac{62}{28} = 2.21\) so lower bound is 3 workers | M1 A1 |
| (2) |
Notes
d1M1 Attempt to find lower bound. [52-72 / their finish time] accept awrt 2.2.
d1A1 CAO – correct calculation seen or awrt 2.2, then . [Beware 28/11 gives 3 also, so 3 with no working gets M0A0.]
| Scheme | Marks |
|---|---|
 | 1M1 1A1 2A1 3A1 |
| (4) | |
| (14 marks) |
Notes
e1M1 Not a cascade chart. 4 ‘workers’ used at most. At least 7 activities. If in doubt send to review.
e1A1 CHKAB correct. C- 14; H – 10; K – 4; A – 5; B – 9. A and B completed by their late finish times. (A by time = 18 B by time = 21).
Now you need to check the last 6 activites – the last two marks are for D, E, F, G, I, J only
First check that they have only used three workers and that all 11 activities are present (just once).
Then check precedences: You have these on the mark scheme in (a).
Each row of the table in (a) could give rise to 1 error (only)
I’d suggest you check these ones first since they are most likely to generate errors.
- F must not start until after B and E are complete.
- G must not start until after B and E are complete.
- J must not start until after C, D, F are complete.
- I must not start until after D and F are completed
You need to check the others too of course.
Finally you need to check the length of each activity.
Length 5 - A, I
Length 4 – D
Length 3 – E, G, J
Length 2 – F
Length 9 – B
e2A1 3 workers. All 11 activities present (just once). Condone one error either precedence, or activity length, on activities D, E, F, G I, J.
e3A1 3 workers. All 11 activities present (just once). No errors on activities D, E, F, G I, J.
Please use the pen or highlighter tool to indicate any errors to your team leader.
Usually we use a vertical line to indicate precedence errors, indicating the overlap, and a horizontal line to indicate an activity of incorrect length.