Person 1 can do a certain job in 21 minutes, and person 2 can do the same job in 28 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 21 minutes, and person 2 can do the same job in 28 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

anonymous · Answer

Think of it as a distance problem. dist. = rate*time
In this case dist. = 1 (One job). time is 21 min. so we have$$1=21r$$ Rate is 1 job per 21 min. so we have $$r={1\over21}$$

anonymous · Answer

here's a question. How long would it take if both person one and two worked on the same house at the same rates as they are in the original problem?