



 
Hi Tan, Suppose you add $X$ ml of 96% sulphuric acid then you will be adding $0.96 \times x$ ml of pure acid. Suppose you add it to $Y$ ml of 30% sulphuric acid which contains $0.30 \times Y$ pure acid. You then have $X + Y$ ml of a mixture which you want to be 50% pure acid. Hence \[0.96 X + 0.30 Y = 0.50 (X + Y).\] If you know $Y$ you can solve for $X.$ Write back if you need more assistance,  


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