T1 exec. first and take 1 out of 5 processor to execute.. Efficiency = 1/5 * 100 = 20%
T2 takes 1 out of 5 processor to execute.. Eff. = 1/5*100 = 20%
T3,T4 and T5 will execute in parallel and all will take same amt. Of time... So they will use 3 out of 5 processors to execute.. Eff. = 3/5*100 = 60%
T6,T7 and T8 will also do the same... And will take 3 out of 5 processors to execute... Eff. = 3/5* 100 = 60%
Avg eff. = (20+20+60+60)/4 = 160/4 = 40% ans