CPU Clock Cycle Time= 10^-9 sec =1nsec
Each interrogation and transfer take =800*1ns=800nsec
In 1 sec keyboard is interrogated 10 times
So in 1 nsec it is interrogated =10 ×10^(-9) times
So, total time spent in polling=800*10*10^(-9) nsec
% of time spent in polling=((time spent on polling in a cycle)/(total time) )*100
=(((800*10^(-8))nsec)/(1nsec)) *100
=0.0008