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

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### Question

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?

A

\$4{146/211}\$ mins.

B

\$5{151/210}\$ mins.

C

\$3{140/213}\$ mins.

D

\$7{44/71}\$ mins.

Soln.
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.