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?
Original volume 1000 cc 200 is water ( 1/5 is water)
draining 150 removes 1/5 * 150 = 30 cc water now there is 170 water
add 150 water now there is 320 water in 1000 cc
draining 250 removes 320 /1000 * 250 = 80 cc water Now there is 240 water
adding 250 cc water makes 490 water in 1000 cc