From a sample containing 200 ml of sodium hydroxide, 20 ml was taken out and was replaced with water. Again, 40 ml of mixture was taken out and replaced with water. Finally, 50 ml of mixture was taken out and replaced with water. Find the quantity of water in the final mixture.

Using the successive replacement formula, the remaining quantity of sodium hydroxide is 200 multiplied by (1 minus 20/200), (1 minus 40/200), and (1 minus 50/200). This calculates to 200 multiplied by 9/10, 8/10, and 3/4, yielding 108 ml of sodium hydroxide. The final mixture is 200 ml in total, so the quantity of water is 200 minus 108, which is 92 ml.

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