One person can do a certain job in twenty-one minutes, and another person can do the same job in twenty-eight minutes. How many minutes will it take them to do the job together?

6 min
12 min
24 min

Question

One person can do a certain job in twenty-one minutes, and another person can do the same job in twenty-eight minutes. How many minutes will it take them to do the job together?

6 min
12 min
24 min

anonymous · Answer

12 min

anonymous · Answer

:)

radar · Answer

12 min use product over sum
(21X28)/49

anonymous · Answer

iN 1 min the first person can finish 1/21 of the work
in 1 min the second person can finish 1/28 of the work
                                                                      1             1                49
Together in 1 minute they can finish = ----  +  ------  = -------
                                                                     21             28            588

                                                                               588  min
So to finish the complete work they will take -------  =  12 min
                                                                                 49