SOLUTION: One printing press can print the first edition of a book in 28 min, whereas a second printing press requires 70 min to print the same number of copies. How long would it take to pr

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Question 451511: One printing press can print the first edition of a book in 28 min, whereas a second printing press requires 70 min to print the same number of copies. How long would it take to print the first edition with both presses operating?
Answer by pedjajov(51) About Me  (Show Source):
You can put this solution on YOUR website!
First press prints 1%2F28 of the book in a minute while the second press does 1%2F70 of the book in a minute.
Working together they will print
1%2F28+%2B+1%2F70 = 5%2F140+%2B+2%2F140 = 7%2F140 = 1%2F20
Now we can make a proportion that 1%2F20 of the book both presses print in a minute and we want to find out how long it takes both presses to print one book:
1/20 book : 1 minutes = 1 book : x minutes
1/20 * x = 1 * 1
x = 1 * 1 / (1/20)
x = 20 minutes