A jar contains a mixture of two liquids A and B in the ratio 4 : 1. When 10 litre of the mixture is replaced with liquid B, the ratio becomes 2 : 3. The volume of liquid A present in the jar earlier was:
$$\frac{QNR}{total} = \frac{QNR(initial)}{total} (1- \frac{\textrm{Replaced Quantity}}{total})$$
QNR is the quantity which has not entered again
so here QNR is A
$$\frac{A}{5x} = \frac{4x}{5x} (1- \frac{10}{5x})$$
A = 4(x- 2)
B = 5x - 4x + 8 = x+3
$$\frac{4x-8}{x+3} = \frac{2}{3}$$
12x - 24 = 2x + 6
10 x = 30
x = 3
so volume = 5x = 5 x 3 = 15 ltr
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