MadeEasy Subject Test: CO & Architecture - Io Handling

Question

 

The solution says that the answer should be 80, but applying the formula (x/y)*100, where x is 250 and y is 200 fraction comes out to be greater than 1. Am i making a mistake in interpreting x and y here?

Comments

What % of processor time is consumed by I/O device means % of time CPU is idle. right?
Now this is given by:

        Data transfer time (say y)
_______________________________
Data Preparation time(say x)  +   y

Isn't this should be the case?

Answer 1

Total time = (200+250)us = 450 us.

Processor involvement time = 250 us.

% of cpu time =(250/450)*100 = 55.56%

So ans should be (d).