51.0 mL of a 1.20 M solution is diluted to a total volume of 248 mL. A 124-mL portion of that solution is diluted by adding 125 mL of water. What is the final concentration? Assume the volumes are additive.

1 answer

How many mols did you start with? That's M x L = 1.20 x 0.051 = 0.0612 and that is in 248 so the concn of the first solution is 0.0612/0.248 = about 0.25 but you should redo it for more accuracy.
Then 124 mL of that is diluted.
New concn is about 0.25 x [(124/(124+125)] = ?