SOLUTION: If a+b=10 and a+c=20, find a+b+c.

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Question 984698: If a+b=10 and a+c=20, find a+b+c.
Answer by Boreal(15235) About Me  (Show Source):
You can put this solution on YOUR website!
a+b=10
-a-c=-20
b-c=-10

a+b=10
a=10-b
;
a+c=20
a=20-c
;
a+b+c=20-c+b+c=20+b
but b=10-a
a+b+c=30-a
b+c=30. But b-c=-10
2b=20; b=10
;
a=0
b=10
a+b+c=20+b=30
c=20
;
answer is 30.