AS June 2019 Q3

EdexcelAS paperCurrent spec7 marksCritical Path Analysis

Activity	Immediately preceding activities
A	-
B	-
C	A
D	A
E	A
F	B, C
G	B, C
H	D
I	D, E, F, G
J	D, E, F, G
K	G

(a) Draw the activity network described in the precedence table above, using activity on arc. Your activity network must contain the minimum number of dummies. (5)

Every activity shown in the precedence table has the same duration.

(b) Explain why activity B cannot be critical. (1)

activity network: A and B from the start; C from the end of A to the end of B; D and E from the end of A; F and G from the end of B; dummies from the end of D and from the end of G into the end of E and F; H from the end of D; I and J from the end of E and F; K from the end of G; a final dummy joining the ends of H and I to the finish — Mark scheme (a)

Scheme	Marks	AO
	M1 A1 A1 A1 A1	1.1b 1.1b 1.1b 1.1b 1.1b
	(5)

Mark scheme (b)

Scheme	Marks	AO
Activity F (and/or G) requires activity B and the two activities A and C to be completed before F (and/or G) can begin. The time to complete A and C is double that of B and so B can be delayed waiting for A and C to be completed and so B is therefore not critical.	B1	2.4
	(1)

Notes

B1: CAO - some mention of the time required to complete A + C compared with B (for the next activity to begin (either F and/or G)) oe e.g. paths through B have a maximum length of 3 (non-dummy) activities and there is at least one path of length 4 which does not include B so B cannot be critical OR the late time for B must be the same as the late time for A + C which is twice the duration of B and therefore B is not critical. Give bod to responses that imply that B and C meet at the same event, but C is also dependent on A (the key point for awarding this mark is that activities A and C imply that B is not critical)

Scheme	Marks	AO
Activities D, E and H	B1	2.2a
	(1)
	(7 marks)