Discussion of Question with ID = 031 under Pipes-and-Cisterns

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Question

Three taps R, G and B are supplying red, green and blue colored inks into a tub. They can independently fill the tub in 7, 3 and 6 minutes. They are turned on at the same time. What is the ratio of blue ink after 3 minutes?

A

${7/27}$.

B

$1{4/13}$.

C

${7/29}$.

D

$3{1/29}$.

Soln.
Ans: a

Let the time taken by them to independently fill the tank be r, g and b minutes. Ink discharged by the blue tap is $3/b$. The total of all the inks is $3/r + 3/g + 3/b$. The ratio is ${1/b}/{1/r + 1/g + 1/b}$, which simplifies to ${rg}/{rg + gb + br}$ = ${7/27}$.

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