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Ruth has a beaker containing a solution of $800$ mL of acid and $200$ mL of water.  She thinks the solution is a little strong, so she drains $150$ mL from the beaker, adds $150$ mL of water, and stirs the solution.  Ruth thinks the solution is still too strong, so again she drains $250$ mL from the beaker, and adds $250$ mL of water.  How many mL of water are now in the beaker?

 Nov 13, 2023
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800mL acid + 200mL water = 1000mL of total liquid.

 

Draining 150mL of total liquid

150/1000 = 15%, which means 15% of the water and 15% of the acid will be drained.

0.85* 800 = 680mL acid

0.85* 200 = 170mL water

= 680mL acid and 170mL water

 

Adding 150mL water

170 + 150 = 320mL water

So there would be 680mL acid and 320mL water.

 

Draining 250mL of total liquid

680 + 320 = 1000mL total liquid

250/1000 = 25%, which means 25% of the water and 25% of the acid will be drained.

0.75*680 = 510mL acid

0.75*320 = 240mL water

 

Adding 250mL water

240 + 250 = 490mL water

So your final answer is 490mL water.

 Nov 13, 2023

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