during an experiment, 20 ml of 4 M hydrochloric acid is mixed with 30 ml of water. what is the concentration of your new solution
20ml of 4M holds .02*4 = .08 moles HCl
Final volume is 50ml, with .08 moles HCl.
.08/.05 = 1.6M
Just consider that you have 5/2 the volume, so 2/5 the concentration.