Subject: Why did the ice melt faster in salt water than in plain water?

I'm helping my 4th grade son do his science fair experiment.  We 
melted ice cubes in plain water and salt water.  Beginning water 
temperatures were the same for all water (about 58F).  Ending 
temperatures were about 42F for plain water and 48F for salt 
water.  It took an average of 13 min for the ice cube to melt in 
plain water and 43min for the same size ice cube to melt in salt 
water. WHY?  Room temperature, volumes, etc. were all the same.  
I read S. Conway's response from 3/8/98 but that really didn't 
give me enough information.  Can someone help me so that I can 
explain this to a 9 year old?  Thanks!!

Re: Why did the ice melt faster in salt water than in plain water?