average weight of a+b=45
average weight of b+c=43
average weight of a+c=50
what is the average of a,b,c
you want (a+b+c)/3
(a+b)/2 = 45
(b+c)/2 = 43
(a+c)/2 = 50
Add them up and you have
(a+b+b+c+a+c)/2 = 45+43+50
(2a+2b+2c)/2 = 138
(a+b+c) = 138
(a+b+c)/3 = 46