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If a+b=8, b+c=10 and c+a=12, what is the value of a+b+c?
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Patrick Ivers, former mathematics & English instructor
Answered June 26, 2018
If a+b=8, b+c=10 and c+a=12, what is the value of a+b+c?
The puzzle is solved by defining each variable in terms of another variable & a number & then making substitutions. Begin by taking each sum to define one of the variables in terms of the other. (Different combinations are available, but I’ll follow the a,b,c order.)
a+b=8 becomes a=8-b
b+c=10 becomes b=10-c
c+a=12 becomes c=12-a
Now subtract two of the equations that contain the same variable. I’ll pick two that contain an a: c+a =12 & a+b=8. Subtracting the latter from the former eliminates the “a”s, leaving c-b=4. Adding b to both sides to isolate c gives c=b+4. From above we can take b=10-c to substitute for b in c=b+4, giving us c=(10-c) + 4). Simplify the right side to c=14-c, add c to both sides, giving 2c=14, & then divide both sides by 2 to obtain c=7.
Replace the c in b=10-c with 7 to
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Paul K. Young, Former PhD candidate in Mathematics
Answered September 28, 2016
If A = B and B = C, does A = C?
In mathematics = is assumed to be a transitive relationship. Transitivity means precisely what you stated: A = B and B = C implies A = C.
While it’s possible to use = to represent a non-transitive relationship this would be considered an abuse of notation. A ~ B or R(A, B) would be a better way to express the relation in this case.
Similar assumptions are made about operators like + and *. + is generally assumed to be commutative, whereas * can be used for noncommutative operations like matrix multiplication. E.g. A * B != B * A.
Equality in programming is another story entirely.
In many languages = is the assignment operator and == is the equality operator. Assignment is not transitive - it’s not even a relation.There are cases where the equality operator doesn’t define a transitive relation.
