I need help writing an equation

Question

A student  wants to dilute 35 liters of a 35% salt solution to a 16% solution. How many liters of distilled water does the student need to add to the 35% salt solution to obtain the  16% salt solution ?

 

I'm having trouble writing an equation for this .

Answer 1

You can use the equation of V1C1 = V2C2 where V1 and V2 are initial and final volumes respectively, and C1 and C2 are  initial and final concentrations. Thus (35 L)(35%) = (x L)(16%) and x = 76.6 L. This is the final volume so the volune of distilled water to be added is 76.6 L - 35 L = 41.6 L