Concept:

Average total time is defined as the sum of:

Average seek + Average Rotational Delay + Transfer time

Let us first read the first track:

Average seek time = 4 ms

Average Rotational Delay = 2 ms

Reading 500 sectors per track is also given

The rotational speed is 15000 rpm, i.e.

The time taken in 15000 revolution = 1 min = 60 sec

The time taken in 1 revolution will be:

\(\frac{1}{{15000}} \times 60\;sec\) 

Now, Reading 500 sectors = Time for 1 Revolution = 4 msec

The above is the complete track reading time.

Hence the time required to read the first track will be:

4 ms(average seek) + 2 ms (average rotational delay) + 4 ms (Reading 500 sector) = 10 msec

Now, it is given that sequential organization is followed and no seek time is required for further reading of the remaining 4 tracks.

But the remaining 4 tracks will have a rotational delay and reading time of tracks, i.e.

= 4 × (2 + 4) msec

4  = No. of remaining tracks

2 ms = rotational delay

4 ms = reading time of 500 sectors or 1 track

= 4 × 6 = 24 sec

∴ The total time will be:

= 10 + 24 = 34 msec

 = 0.034 sec