Person 1 can do a certain job in twenty-one minutes, and person 2 can do the same job in twenty-eight minutes. When completing the job together, which expression would be used to represent the amount of work done by person 1?

21
1/21
x/21
21x

Question

Person 1 can do a certain job in twenty-one minutes, and person 2 can do the same job in twenty-eight minutes. When completing the job together, which expression would be used to represent the amount of work done by person 1?

21
1/21
x/21
21x

radar · Answer

Person 1, can do 1/21 of the job in one minute.  This is pointed out in the solution of the problem posted directly above this one.