It is different because you are doing a different method to complete the problem. It is the same because it ends up with the same answer, provided you complete the process correctly.
Answer:r'=0.327 m
Step-by-step explanation:
Given

angular velocity 
mass of objects 
distance of objects from stool 
Combined moment of inertia of stool and student 
Now student pull off his hands so as to increase its speed to 3.60 rev/s


Initial moment of inertia of two masses 

After Pulling off hands so that r' is the distance of masses from stool

Conserving angular momentum








Step-by-step explanation:
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Answer:
10
Step-by-step explanation:
It would take 1minute and 10 seconds to complete the job because you have to subtract 2hours (2:00) by 90seconds (0:90)