A certain assembly project requires the completion of each of 5 tasks

Question

https://gmatclub.com/forum/download/file.php?id=74918 A certain assembly project requires the completion of each of 5 tasks. In the diagram, the tasks are represented by circles labeled A–E and the number above each circle represents the number of days needed to complete the task. Arrows indicate prerequisite tasks. For instance, the arrow from Task A to Task C indicates that Task A must be completed before Task C can be started. Unless otherwise prohibited by these constraints, several tasks can be worked on at the same time. The project is complete once all 5 tasks are completed. Use the drop-down menus to create the most accurate statements based on the information provided. The least number of days needed to complete the project is GRAPH_1_PLACEHOLDER days. If the number of days needed to complete Task C is increased by 1 day, then the least number of days needed to complete the project GRAPH_2_PLACEHOLDER . ID: 100439 A certain assembly project requires.png

GMATCoachBen · Accepted Answer

Video solution here:

https://www.youtube.com/watch?v=fyFew7uNZgg

krish74_ · Answer

A. Apply

The diagram indicates that both Tasks A and D can begin immediately, since neither task has any other task as a prerequisite. Task A will require 8 days to complete, at which point Task B can begin. After another 5 days Task B will be completed, and Task C can then begin. Task C cannot begin earlier than 13 days into the project because both Tasks A and B are prerequisites to Task C. After 20 days (8 + 5 + 7 = 20), Task C will be completed. However, Task E cannot begin until Tasks C and D have been completed, and Task D needs 21 days to complete. Finally, Task E would require 5 additional days, bringing the least number of days required to complete the project to 26 (21 + 5 = 26).

The correct answer is 26.

B. Apply

As discussed above, Task C cannot begin until at least 13 days after the beginning of the project. The diagram indicates that Task C takes 7 days to complete, and if the number of days needed to complete Task C increased by 1 day, then the total number of days needed to complete Tasks A, B, and C would be 21 (8 + 5 + 8 = 21). However, since both Task C and Task D are prerequisites to Task E, the increase from 20 days to 21 days would not increase the total number of days needed to complete the project, because 21 days were already needed before Task E could begin.

The correct answer is remains the same.

Oppenheimer1945 · Answer

Best is to look out for all paths from Begin to End and sum up no of days.

1) The longest task is route DE: 21+5=26 days

2) The route ACE takes 8+7+1+5=21 days, but this is less than route De(26 days). hence Remains the same

whatsarc · Answer

Will there be such questions on the DI Section?

Oppenheimer1945 · Answer

Highly likely. !

kush4 · Answer

Please guide me with my doubt, it is written the project is complete once all 5 tasks are completed,
So the we have to include all the tasks to complete the project? But there is no way to go through all the tasks because arrows restrict them.

UmerShariff · Answer

why cant it be A to B and end i.e 13.

bb · Answer

First sentence of the question: A certain assembly project requires the  completion of each of 5 tasks .

MoPouyan · Answer

I've got confused. What does  least  mean here?

"The least number of days needed to complete the project is --------- days."

D3N0 · Answer

Minimum number of days in which all the 5 tasks would be completed to reach the end from the beginning. 
Note: task can be completed simultaneously but the restriction is "prior task has to end before the task at the next node can begin. So basically you are looking to find the path through which you can complete all the tasks in minimum days.

Run990919 · Answer

I am quite confused as why task C cannot start right away as there is an arrow pointing from begin to task C "Directly" - same as that to Task A and D

bb · Answer

Because the question says that the arrows work different from what you expected.

Here’s a quote from the question. Did you see it?

Run990919 · Answer

Grateful for your kind response. So does it mean that whether that arrow pointing from 'begin' to 'C' will be available has no effects anyway?

bb · Answer

Yes. It seems that the arrow doesn’t mean the process but rather dependency so in this case the arrow from begin to C is indeed meaningless.

This is a good mistake to learn so you avoid jumping to conclusions on questions, at least until you read the question fully.

bishal128 · Answer

HakunamaTaTA...great explainer. Thx

JainamS · Answer

(1) The important detail in the question is that "several tasks can be worked on at the same time". So while Tasks A, B & C are done in 20 days combined, Task D can run simultaneously taking 21 days followed by Task E taking 5 days, in total 26 days.

(2) Increasing Task C by 1 day, increases the total days to 21 (for A, B & C combined) which is the same as Task D, and followed by Task E (5 days) - the least no. of days remainds unchanged at 26 days.

anchitadiwan · Answer

Exactly, because A, C, and D started at the same time.

A certain assembly project requires the completion of each of 5 tasks

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A certain assembly project requires the completion of each of 5 tasks