Answers

2016-06-26T01:08:11+08:00
 [(b+2)+(4b+5)]/2   =  b+2       / arithmetic mean of x and y = (x+y)/2
 (5b+7)/2  = b+2
  5b +7 =   2(b+ 2)
   3b  = 4 -7  =  -3
    b = -1
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