So, here you have to look at the periodic table and see what the molar mass of each molecule composing the water compound 

its two hydrogen atom plus an oxygen molecule, making it about 18g per mol.
That said, looking at the mass, we have to ask ourselves, if a mol of water contains 18g of mass, how many moles do we have in 0.5g of water? 
We just do a cross multiplication:
 
 
        
        
        
23308 is the answer of how many is even with no repitition
        
             
        
        
        
Answer:
-4,-4
Step-by-step explanation:
 
        
             
        
        
        
Answer:
only students who have recess at 12 p.m. or later may go out
Step-by-step explanation:
Let the time after midnight be represented by t, and the temperature be y. Since the temperature increases by 1.2 degrees Fahrenheit each hour, the time taken to reach 32 degrees Fahrenheit can be gotten from:
y = 1.2t + 18
put y = 32
32 = 1.2t + 18
1.2t = 14
t = 14/1.2 = 11.67 hours
Since the recess starts at half hour or hour, hence the recess would start at t = 12 hours, i.e. at 12 p.m.
Hence only students who have recess at 12 p.m. or later may go out