Correct Answer - Option 2 : 0.75 sec

The correct answer is **0.75 sec.**

Average seek time for a random location time is given as 10 ms. The average rotational latency is half of the time needed for complete rotation. It is given that 6000 rotations need 1 minute. So one rotation will take 60/6000 seconds which is 10 ms. Therefore average rotational latency is half of 10 ms, which is 5ms.

Average disk access time = seek time + rotational latency

= 10 ms + 5 ms = 15 ms

For 50 libraries, the average disk access time will be 15*50 ms =750ms

1 sec = 1000 ms

750 divide the time value by 1000 =0.75

**Therefore option 2 is correct**