Discussion of Question with ID = 094 under Pipes-and-Cisterns

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Two taps X, Y and Z can fill a tank in 18, 15 and 11 minutes respectively. All the taps are turned on at the same time. After how many minutes is the tank completely filled?


$4{146/211}$ mins.


$5{151/210}$ mins.


$3{140/213}$ mins.


$7{44/71}$ mins.

Ans: a

Let the time be x mins. Then sum of works done by X, Y and Z = 1. $x/18 + x/15 + x/11 = 1$. Solving, we get x = $4{146/211}$. Or use the shortcut ${abc}/{ab + bc + ca}$. Another thing, instead of solving the entire calculation, you can keep an eye on the options to find the nearest answer.

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