Symbiosis National Aptitude Test SNAP 2019 Paper

After replacing 6 litres of milk by water, the container contains (x – 6) litres milk and 6 litres water.
Ratio of Milk : Water = (x – 6) : 6
Again, Mohan replaced 6 litres of mixture by 6 litres of water.
So, quantity of milk remains
= (x - 6) - 6 × $\frac{\left(\mathit{x}+6\right)}{\mathit{x}}$
= $\frac{{\left(\mathit{x}+6\right)}^2}{\mathit{x}}$
Quantity of water = 6 - 6 × $\frac{6}{\mathit{x}}+6$
= $\frac{12}{\mathit{x}}\left(\mathit{x}-3\right)$
ATQ,
$\frac{{\left(\mathit{x}-6\right)}^2}{\mathit{x}}:\frac{12}{\mathit{x}}\left(\mathit{x}-3\right)$ :: 9 : 16
$\frac{{\left(\mathit{x}-6\right)}^2}{12\left(\mathit{x}-3\right)}$ = $\frac{9}{16}$
$4{\left(\mathit{x}\mathit{–}6\right)}^2$ = 27(x – 3)
$4{\mathit{x}}^2$ – 75x + 225 = 0
(4x – 15)(x – 15) = 0
∴ x = 15 litres.