Question 1153
Sol: Assume there were x studented attended,so their average was 500/x dollars.
     Since there were x + 5 students planned (note 5 were absent), the average
     among the planned was 500/(x+5).
     We know the difference between these two averages is 5, we have 
         
     500/x = 500/(x+5) + 5,
     Dividing eqch term by 5: 
     100/x = 100/(x+5) + 1,  
     Multiplying by x(x+5) to cancel the denominator:
      100(x+5) = 100x + x^2 + 5x,
     Simplify:    x^2 + 5x -500 = 0,
     Factoring: (x-20)(x + 25) = 0,
     So,x= 20 or -25(negative, invalid answer) 

     Answer : there were 20 students attended the get-together.