Consider a uniprocessor system executing three tasks T₁, T₂ and T₃, each of which is composed of an infinite sequence of jobs (or instances) which arrive periodically at intervals of 3, 7 and 20 milliseconds, respectively. The priority of each task is the inverse of its period, and the available tasks are scheduled in order of priority, with the highest priority task scheduled first. Each instance of T₁, T₂ and T₃ requires an execution time of 1, 2 and 4 milliseconds, respectively. Given that all tasks initially arrive at the beginning of the 1^st millisecond and task preemptions are allowed, the first instance of T₃ completes its execution at the end of _____________ milliseconds.

For the processes listed in the following table, which of the following scheduling schemes will give the lowest average turnaround time?

Process	Arrival Time	Processing Time
A	0	3
B	1	6
D	4	4
E	6	2

Three processes $$A, B$$ and $$C$$ each execute a loop of $$100$$ iterations. In each iteration of the loop, a process performs a single computation that requires $${t_c}\,\,CPU$$ milliseconds and then initiates a single $${\rm I}/O$$ operation that lasts for $${t_{io}}$$ milliseconds. It is assumed that the computer where the processes execute has sufficient number of $${\rm I}/O$$ devices and the $$OS$$ of the computer assigns different $${\rm I}/O$$ devices to each process. Also, the scheduling overhead of the $$OS$$ is negligible. The processes have the following characteristics:

Process id	tc	tio
A	100 ms	500 ms
B	350 ms	500 ms
C	200 ms	500 ms

The processes $$A, B,$$ and $$C$$ are started at times $$0, 5$$ and $$10$$ milliseconds respectively, in a pure time sharing system (round robin scheduling) that uses a time slice of $$50$$ milliseconds. The time in milliseconds at which process $$C$$ would complete its first $${\rm I}/O$$ operation is __________.

An operating system uses $$shortest$$ $$remaining$$ $$time$$ $$first$$ scheduling algorithm for pre-emptive scheduling of processes. Consider the following set of processes with their arrival times and $$CPU$$ burst times (in milliseconds):

Process	Arrival Time	Burst Time
P1	0	12
P2	2	4
P3	3	6
P4	8	5

The average waiting time (in milliseconds) of the processes is ________.