Question 507800
    One secretary can do a particular typing job in 6hr and another secretary can do same job in 4hr. How long will it take if the job is done by the two secretaries working together? 
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Let x = time (hours) it takes for both
then
x(1/6 + 1/4) = 1
multiply both sides by 12 (common denominator):
x(2 + 3) = 12
x(5) = 12
x = 12/5
x = 2.4 hours
or
x = 2 hours and 24 minutes