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 200 mL from the beaker, adds 200 mL of water, and stirs the solution. Ruth thinks the solution is still too strong, so again she drains 200 mL from the beaker, and adds 200 mL of water. How many mL of water are now in the beaker?
starts out 1/5 water (200 out of 1000ml)
so 1/5 of the 200ml drained off is water..... leaving 160 ml water
then 200ml water is added so there is now 160 + 200 = 360 ml water
then she drains off 200 ml this 200 ml is 360/1000 water = 72 ml of water drained off leaves 360 - 72 = 288 ml
then she adds 200 ml water 288 + 200 = 488 ml waer in final solution
