Question 602969
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Hi,
It takes Nina 3 hours to proof a chapter of Hawkes Learning Systems' Statistics
 book and it takes Cynthia 12 hours.
Let x represent the time it would take them together
Note: job / hour is the key
 1/3 + 1/12 = 1/x       |Multiplying thru by 12x so as all denominators = 1
4x + x = 12
   5x = 12
    x = 2.4 hrs, the time it would take them together