SOLUTION: the average of 11 results is 30,that of the first five is 25 and that of the last five is 28.the value of 6th number is?

Question 776674: the average of 11 results is 30,that of the first five is 25 and that of the last five is 28.the value of 6th number is?
Answer by AnlytcPhil(1806) (Show Source): You can put this solution on YOUR website!
the average of 11 results is 30,that of the first five is 25 and that of the last five is 28.the value of 6th number is?

Let the 11 results be a,b,c,d,e,f,g,h,i,j,k

>>...the average of 11 results is 30,...<<



Multiply both sides by 11

a+b+c+d+e+f+g+h+i+j+k = 330

>>...that of the first five is 25,...<<



Multiply both sides by 5

a+b+c+d+e = 125

>>...and that of the last five is 28...<<



Multiply both sides by 11

g+h+i+j+k = 140

So we have these three equations:

a+b+c+d+e+f+g+h+i+j+k = 330
a+b+c+d+e             = 125
            g+h+i+j+k = 140

Subtract the 2nd equation from the 1st:

          f+g+h+i+j+k = 205

Subtract the third equation from that

          f+g+h+i+j+k = 205
            g+h+i+j+k = 140
          f           =  65

Answer 65.

Edwin

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