When dealing with making diluted solutions from concentrated solutions, we can use the following formula c1v1 = c2v2 where c1 and v1 are the concentration and volume of the concentrated solution respectively. c2 and v2 are the concentration and volume of the diluted solution respectively substituting these values in the above formula, 20 mL x 0.200 M = C x 250.0 mL C = 0.0160 M