Question

How do you prepare a 0.4 M solution of sulfuric acid in water starting with concentrated sulfuric acid (18 M) and water?

Answer 1

How much 0.4 M H2SO4 do you want? say 1000 mL? Then
1000 mL x 0.4M H2SO4 = mL x 18M H2SO4.
Solve for mL on the right.

Answer 2

22.22