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?
a. 21
b. 1/21
c. x/21
d. 21x

Answer 1

The correct answer is:

C) x/21

Explanation:

Since Person 1 can complete the entire job (100% = 1/1 = 1) in 21 minutes, this person can complete 1/21 of the job per minute. This is Person 1's rate. If x is the amount of time it takes both people together to finish the job, then the amount of work Person 1 does would be (1/21)(x) = x/21.