Crane A can unload a ship in 10 hours and crane B can unload it in 14 hours. How long will it take the two cranes to unload the ship working together?

Sep 4, 2016

$\frac{35}{6} \text{ hrs. = 5 hrs., 50 mnts.}$

Explanation:

Crane A can unload a ship in $10$ hrs.

$\therefore \text{ Crane A can unload "1/10" of the ship in } 1$ hr.

Similarly, Crane B can unload $\frac{1}{14} \text{ of the ship in } 1$ hr.

Hence, both the cranes together can unload

$\frac{1}{10} + \frac{1}{14} = \frac{12}{70} = \frac{6}{35}$ of the ship in $1$ hr.

Therefore, both the cranes work together, the ship will be completely unloaded in $\frac{35}{6} \text{ hrs. = 5 hrs., 50 mnts.}$