What solutes will give the largest reduction in volume when dissolved in water
(1) Your calculations are correct.

(2) $\ce{CaCl2}$ has a density of 2.16 kg/L 

           kg        vol(L)
  CaCl2    18.00     8.38
  H2O      41.62    41.62
           -----    -----
           59.62    50.00 L


But when dissolved the solution has a density of 1.300 kg/L, so the total volume is 45.86 L. (Data about $\ce{CaCl2}$ solutions.)