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Say â€˜Aâ€™ amount 50% solution => A / 2 is the acid amount
X amount is taken out from 50% solution => so X / 2 amount of acid taken out
X amount of 30% acid solution added => so 3X/10 amount of acid added
Resultant solution is 40% acid => acid Ratio 40 / 100 = 2 / 5
(Original acid amount â€“ taken out acid amount + added acid amount ) / Total amount = 2/5
=> (A/2 â€“ X/2 + 3X/10)/A = 2/5
=> X = A/2