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

Answer 1

The amount of work (or the rate) done by the first person is 1/21
r = 1/21

Answer 2

`(1)/(21)` would be used to represent the amount of work done by person 1.

Explanation:

When someone does a work in x time,

Then, the work done by the person in one day =
`(1)/(x)`

Given,

Time taken by person 1 = 21 minutes

Thus, by the above statement,

The one day work of person 1 =
`(1)/(21)`

Hence,
`(1)/(21)` would be used to represent the amount of work done by person 1.

Second option is correct.