Two vessels contain spirit and water mixed respectively in the ratio of 2 : 1 and 3 : 7. Find the ratio in which these are to be mixed to get a new mixture in which the ratio of spirit to water is 7: 9.

A 5 : 11

B 3 : 5

C 5 : 6

D 2 : 1

E None of the above

Solution

Correct Answer: Option B

Vessel 1:

Spirit : water = 2:1

∴ Quantity of spirit =  \(\frac{2}{{2 + 1}}\)

∴ quantity of spirit in one unit = 2/3

Similarly, quantity of water in one unit = 1/3

Vessel 2:

Spirit : water = 3:7

Therefore quantity of spirit in one unit = \(\frac{3}{{10}}\)

And quantity of water in one unit= \(\frac{7}{{10}}\)

Let vessel 1 and vessel 2 contents be mixed in the ratio x : y

Thus according to the new condition, spirit : water = 7 : 9

\(\frac{{\left( {x \times \frac{2}{3}} \right)\; + \left( {y \times \;\frac{3}{{10}}} \right)}}{{\left( {x \times \frac{1}{3}} \right) + \left( {y \times \frac{7}{{10}}} \right)}} = \frac{7}{9}\)

\(\frac{x}{y} = \;\frac{3}{5}\)

Thus the contents of vessel 1 and 2 should be mixed in the ratio 3 : 5

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