What volume of a 2.00 M stock solution of NaOH is needed to prepare 150. mL of 0.40 M solution?

To find the volume ratios we say m1v1=m2v2

where m1 is the initial molarity, m2 the final molarity, v1 the initial volume, v2 the final volume. in this question m1=2.00M, m2=0.40M v2=150ml

Therefore the expression becomes: 2.00M*v1=0.40M*150mL

v1 = (0.40M*150mL) / 2.00M

=30mL