Question

$\begin{array}{ccc}\text{Event numbers}& \text{Activity}& \text{Duration}\\ 1-2& A& 5\\ 1-3& B& 6\\ 2-3& C& 3\\ 2-4& D& 8\\ 4-5& \text{Dummy}& 0\\ 3-5& E& 2\\ 3-6& F& 11\\ 4-6& H& 1\\ 5-6& G& 12\end{array}$

Red flagged activities are

Answer 1

$\begin{array}{cc}\text{Path}& \text{Duration}\\ ADH& 5+8+1=14\\ ADG& 5+8+12=25\leftarrow \text{Critical path}\\ ACEG& 5+3+2+12=22\\ ACF& 5+3+11=19\\ BEG& 6+2+12=20\\ BF& 6+11=17\end{array}$

Critical activities cannot be red flagged.

For red flagging

$\text{Free Float > Total Float}$

(They are essentially non critical activities)

$\underset{–}{\text{ACTIVITY-B}}$

$\text{TF - LFT - EST - Duration}$

$=11-6-0=5$

$\text{FF = TF - Head event slack}$

$=5-(11-8)=2$

$\underset{–}{\text{ACTIVITY-C}}$

$\text{TF = LFT - EST - Duration}$

$=11-5-3=3$

$\text{FF = TF - Head event slack}$

$=3-(11-8)=0$

For activities B & C

FF > TF hence they can red flagged .