Question

a 30.0 ml solution of potassium nitrate was diluted to 125 ml and 25 ml of this solution were then diluted to 150 ml. the concentration of the final solution is 0.00307 M. Calculate the concentration of the original solution.

Answer 1

xM*(30/125)*(25/150) = 0.00307

Answer 2

i do not know if this is right but this is how i would do it.

M1V 1=M2V2.

(0.00307 M) X (150ml)= (M2) X (30 ml)

and then you solve to get m2

Answer 3

Sarah's method will work if you do it TWICE; once for each dilution.
0.00307*150 = 25*c
c = ??
??*125 = 30c
c = xx.
You should arrive at the same answer either way.