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John can complete a task in 6 hours, and Mark can complete the same task in 8 hours. How long will it take for both of them working together to finish
Question

John can complete a task in 6 hours, and Mark can complete the same task in 8 hours. How long will it take for both of them working together to finish the task?

A.

315\frac{31}{5}​ hours

B.

2111 \frac{21}{11}​ hours

C.

407 \frac{40}{7}​hours

D.

247 \frac{24}{7}​hours

Correct option is D

Given:
Time taken by John = 6 hours
Time taken by Mark = 8 hours
Formula Used:
Combined Time = 11T1+1T2\frac{1}{\frac{1}{T_1} + \frac{1}{T_2}}​​
Solution:
Combined Time =116+18 \frac{1}{\frac{1}{6} + \frac{1}{8}}​​
Combined Time = 1424+324\frac{1}{\frac{4}{24} + \frac{3}{24}}​​
Combined Time = 1724\frac{1}{\frac{7}{24}}​​
Combined Time =247 \frac{24}{7}​​
Therefore, both will take 247 \frac{24}{7}​hours to complete the task together.

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