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

In general, when trying to solve work problems, what I usually do is begin with this formula:
\(\dfrac{AB}{A + B} = t\)

Where

A represents time it takes the 1st person to do the job alone
B represents time it takes the 2nd person to do the job alone
t represents the time it takes both to do the job together.

However in this case, they want you to set it up this way:
\(\dfrac{1}{A} + \dfrac{1}{B} = \dfrac{1}{t}\)

Answer 2

@JT

Answer 3

I think that it's x/21

Answer 4

@Hero

Answer 5

Not correct