hi,

first of all the criical path is Start, C(3), D(6), E(8), B(5), End = 22 at this time if we consider Start, C(3), D(6), E(8), F(3), End then the total duration will be 20. Now if B will take 3 days, then B & F will be taking same duration  & we will have 2 critical paths both will take 20 days. Hence option B is ruled out. A being not part of critical path will have same float before & after which is 6 days. Hence option D is ruled out. Option C I donot understand...it's not clear. I belive option A is correct. if F starts immediately then crital path time will be less I am asuming that immediately means taking less time. So it will be < 20 days...so this should be the right answers.

mr boumbo,

you have done analytical part correctly

but concluded wrongly

in second case (after placing 3days) there will be 2 critical paths why you are adding the previous case critical path

in first case one critical path - c-d-e-b-=18,while other 2 noncritical  cdef=16, cdeb=16

in second case 2 critical path -cdeb and cdef =16, while path cab is not critical  =14

Now

by elemination technique

option b is not correct

option c has no meaning

option d - check whether float increase , it is not increasing, becuase

in 1st case project duration = critical path days = 18, where as backword pass at A =18-5 =13

float case 1 at A =13-8-3= 2days

in 2nd case project duration = critical path duration = 16, whereas backword pass atA = 16-3 =13

float case 2 at A = 13-8-3 =2days

hence d is alo not correct

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option A saying it completed sooner, yes it is right, only the second part of this option is not so correct.

but other options are totally wrong hence it is correct.