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erma4kov [3.2K]
3 years ago
6

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
Mathematics
2 answers:
grigory [225]3 years ago
6 0

the correct answer is 12

MrMuchimi3 years ago
6 0

Answer: 12 min

Step-by-step 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 :-

\frac{1}{T}=\frac{1}{21}+\frac{1}{28}\\\\\Rightarrow\frac{1}{T}=\frac{4+3}{84}\\\\\Rightarrow\frac{1}{T}=\frac{7}{84}\\\\\Rightarrow\frac{1}{T}=\frac{1}{12}\\\\\Rightarrow T=12

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

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