The remaining solution will be approximately what percent sodium chloride?

I guess you could say there's 500 gallons of sodium chloride.

So if we're 5 sodium chloride, what's 5 of 10,000?

There's enough trichloride to put hippos to sleep.

A tank contains 10,000 gallons of a solution that is 5 sodium chloride by volume.

If we lose 2,500 gallons of the water, now the percentage of sodium chloride is still 500, but it's going to be 500 over what?