In this task, you need to answer the given multiple-choice question on the general math. Classify your answers into 'a', 'b', 'c', 'd', and 'e'.

Q: Problem: working simultaneously and independently at an identical constant rate , 5 machines of a certain type can produce a total of x units of product p in 4 days . how many of these machines , working simultaneously and independently at this constant rate , can produce a total of 2 x units of product p in 2 days ? 
Options: a ) 11 , b ) 13 , c ) 15 , d ) 18 , e ) 20

A: e
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Q: Problem: what is 2 3 / 4 - 1 2 / 5 divided by 2 / 3 - 1 / 3 ? 
Options: a ) 17 / 36 , b ) 36 / 17 , c ) 7 / 6 , d ) 27 / 20 , e ) 51 / 44

A: d
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Q: Problem: a case of 12 rolls of paper towels sells for $ 9 . the cost of one roll sold individually is $ 1 . what is the percent r of savings per roll for the 12 - roll package over the cost of 12 rolls purchased individually ? 
Options: a ) 9 % , b ) 11 % , c ) 15 % , d ) 25 % , e ) 90 %

A:
d
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