Question

A can contains a mixture of two liquids A and B is the ratio 7 : 5. When 9 litres of mixture are drawn off and the can is filled with B, the ratio of A and B becomes 7 : 9. How many litres of liquid A was contained by the can initially?

Answer 1

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Solution

Let the can initially contain 7x litre and 5x litre of mixture A and B respectively.
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Thus out of 12x litre of total mixture, 9 litre were taken out. 
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Quantity of A in mix. left
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= 7x - 9/12x * 7x
$<b><font face=copper black size =4 color=orange>$
= 28x-21 / 4 litre
$<b><font face=copper black size =4 color=purple>$
Quantity of B in mix. left
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= 5x- 9/12x*5x 
$<b><font face=copper black size =4 color=red>$
= 20x-15 / 4 litre
$<b><font face=copper black size =4 color=blue>$
Therefore ratio 
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7:9
$<b><font face=copper black size =4 color=green>$
or x = 3