Sinc the boy started reading between 3-4 0'clock therefore the hour hand should be between 3-4
and the boy stopped reading between 5-6 o'clock therefore the hour hand should be between 5-6
now since the boy found that the hands are interchanged
then first hour hand was between 3-4 then it is between -6 it is only possible only and only if the minute hand is first between 5-6
therefore the starting will be 3:25 pm and the stopping time will be 5:15 pm
the total time he read is 1 hour 50 min...