OpenStudy (anonymous):

A deck of 320 punched cards can be read by one reader in 20 minutes. A second reader can read the same deck in 12 minutes. How many minutes would it take both readers working together to read a deck? How long would it take to process the deck of cards in example one if the first reader stopped working after 5 minutes?

5 years ago
OpenStudy (anonymous):

I got the first one which is 7.5 mins but i cant get the second part of the problem

5 years ago
OpenStudy (anonymous):

7.5 min, is correct. :)

5 years ago
OpenStudy (anonymous):

ya but what about when the first reader stops reading after 5 mins

5 years ago
OpenStudy (mertsj):

The first reader does 1/20 of the job per minute so in 5 minutes it does 5/20 or 1/4 of the job. The second reader does 1/12 job per minute so in 5 minutes it does 5/12 of the job. So after 5 minutes 1/4+5/12 of the job is done. That is 2/3 of the job. So now the question becomes...how long will it take the second reader to do 1/3 of the job. When you get that answer, add 5 minutes and you will have the answer to the second part.

5 years ago