Initial Ratio of Dye to Water: $2:3$
Represent dye as $2x$ and water as $3x$.
Total Solution: $2x + 3x = 5x = 40$ litres
Solving for x: $x = 8$
Water is added to achieve a new ratio of $2:5$, with the dye amount remaining at $16$ litres.
Let the new water quantity be $w$:
$\frac{16}{16 + w} = \frac{2}{5} \Rightarrow 5 \cdot 16 = 2(w + 16)$
$80 = 2w + 32 \Rightarrow 2w = 48 \Rightarrow w = 24$
Therefore, new water volume = 24 (added) + 24 (original) = 48 litres
New Total Volume = 16 (dye) + 48 (water) = 64 litres
One-fourth of the solution is removed: $\frac{1}{4} \cdot 64 = 16$ litres
The removed 16 litres, maintaining the $2:5$ ratio, consists of:
Remaining solution:
The objective is to achieve a new ratio of $2:3$:
Let the additional dye to be added be $y$, such that:
$\frac{11.429 + y}{36.571} = \frac{2}{3}$
$3(11.429 + y) = 2 \cdot 36.571$
$34.286 + 3y = 73.143 \Rightarrow 3y = 38.857 \Rightarrow y \approx 12.95$
Alternatively, using simplified ratio segments from earlier calculations:
✅ Final Answer: 8 litres of dye must be added.