Dilution of solutions  

Where,
V1 = Volume of solution before dilution
V2 = Volume of solution after dilution
M1 = Concentration before dilution
M2 = Concentration after dilution
Example:
Calculate the volume of the given solvent added during dilution (V) and the volume after dilution (V2).
Volume Before Dilution (V1): 25 L
Concentration Before Dilution (M1): 10 Mol/L
Concentration After Dilution (M2): 7 Mol/L
Solution:
Apply Formula:
Volume After Dilution (V2) = [(V1 * M1) /M2]
Volume of Solvent Added During Dilution (V) = ( V2  V1 )
Volume After Dilution (V2): 35.714285714285715 L
Volume of Solvent Added During Dilution (V): 10.714285714285715 L