Question: Mike decides he wants to replace his movie collection with digital versions.  He has 600 movies.  A third of the movies are in various series and he knows he can get those for only $6 of the cost of a normal movie by just buying the series together.  40% of the remaining movies are older movies which are $5.  How much does replacing the movies cost if a normal movie costs $10?
Answer: 
There are 600/3=200 movies in series
So he pays 200*6=$1200
He has 600-200=400 movies not in series
400*.4=160 movies are old
So those cost 160*5=$800
400-160=240 movies are neither old nor in series
They cost 240*10=$2400
So the total cost is 1200+800+2400=$4400