RRB Group D 17-Sep-2018 Shift 1 Solved Paper

Question : 9 of 100

Marks: +1, -0

Two valves X and Y separately fill a tank in 20 hours and 30 hours, respectively. Both the valves are opened to fill the tank, but when the tank is one-third full the valve is closed. A leak develops in the tank through which one-third of the water supplied by both the valves leaks out.
The leak is immediately closed and the two valves are again opened. What is the total time taken to fill the tank?

14 hours
10 hours
8 hours
12 hours

Validate

Solution:

Valve

X

fills up

\;{1}/{20^{\;\text "th "\;}}

in one hour
Valve

Y

fills up

\;{1}/{30^{\;\text "th "\;}}

in one hour.

∴

together they fill

\;{1}/{20}+\;{1}/{30}=\;{3+2}/{60}

=\;{1}/{12^{th}}

in one hour
since

\;{1}/{3 {rd}}

of the tank empties due to leak.

∴

Valve

X

and

Y

needs to fill up

1-\;{1}/{3}=\;{2}/{3}

of the tank

\Rightarrow

time taken will be

\;{2 \/ 3}/{1 \/ 12}=\;{24}/{3}=8

hours.

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