GIVEN : 1 hour 1/3 part of work then 21/5 hours = ?
--> This problem can be solved using unitary method
--> In 1 hour he completed 1/3 part of work
--> So in 21/5 hours he completes ?
--> He completes 21/5*1/3 part of work
= 7/5 part of work
= 1 1/5 part of work
Answer: he completed 1 1/5 part of the work in 21/5 hours.