Question

One person can do a certain job in twenty-one minutes, and another person can do the same job in twenty-eight minutes. How many minutes will it take them to do the job together?

6 min
12 min
24 min

Answer 1

the correct answer is 12

Answer 2

Answer: 12 min

Explanation:

Given: Time taken by one person to do a job = 21 minutes

Time taken by another person to do a the same job = 28 minutes

If they work together then the total time taken by both of them to complete the job is given by :-

`(1)/(T)=(1)/(21)+(1)/(28)\\\\\Rightarrow(1)/(T)=(4+3)/(84)\\\\\Rightarrow(1)/(T)=(7)/(84)\\\\\Rightarrow(1)/(T)=(1)/(12)\\\\\Rightarrow T=12`

Hence, they will take 12 minutes to do the job together.