How many ml of a 2.0 m nabr solution are needed to make 200.0 ml of 0.50 m nabr?

To solve this we use the equation,

M1V1 = M2V2

where M1 is the concentration of the stock solution, V1 is the volume of the stock solution, M2 is the concentration of the new solution and V2 is its volume.

2.0 M x V1 = 0.50 M x 200 mL

V1 = 50 mL needed