0ml of a 1.20 m solution is diluted to a total volume of 228 ml. a 114-ml portion of that solution is diluted by adding 111 ml of water. what is the final concentration? assume the volumes are additive.

54.0 ml of a 1.2 m solution was diluted to a total volume of 228 ml
USing dilution equation
M1V1 = M2V2
Where M1V1 is before dilution while M2V2 is after dilution.
Therefore;
M1= 1.20 M, V2= 54 ml,  
M2=              V2 = 228 ml

1.20 M × 54 ml = M2 × 228 ml
  M2 = (1.2 ×54)/ 228 ml
       = 0.2842 M

0.2842 × 114 ml = M2 × (114 +111)
      M2 = (0.2842 ×114)/ 225
            = 0.143995
            = 0.144 M

Ithink about 50 % of an original isotope's number of atoms remain

The answer is just took the test