Question 370254
without music = 3 per hour
total 12 problems
completion time = 5 hours
..
Starts with music on 
3 hours music on and 2 hours without music.
In 2 hours he will do 2*3 = 6 problems.
Balnce 6 problems in 3 hours
so with music he does 2 problems per hour.
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m.ananth@hotmail.ca