
Nataliya D. answered 08/12/13
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This kind of problem requires to use associative and commutative properties of addition.
a + b + c = (a + b) + c = a + (b + c)
a + b = b + c
~~~~~~~~~~~
(33 + 45) + 7 =
33 + 45 + 7 =
45 + 33 + 7 =
45 + (33 + 7) =
45 + 40 = 85