19
YOUR ANSWER: The sentence 1 + 2 = 3 is false.
The words "true" and "false" have a rather special meaning in mathematics. With the meanings usually attached to the symbols 1, 2, and 3, the sentence or equation
1 + 2 = 3
is true; that is, it is consistent with our definitions of the symbols 1, 2, and 3. This is a perfectly circular argument, of course, since our definition of the symbol 3 is likely to depend on the statement 1 + 2 = 3 (unless we are very sophisticated mathematicians; then we put the circularity of the argument someplace else, where it's harder to spot). But in general, when we say a mathematical statement is true, we simply mean that it is consistent with the definitions of the symbols used and doesn't get us into any contradictions later on. This is all that is meant by saying that a mathematical statement is true.
This cheerful acceptance of consistency as the test of truth in mathematics is maddening to people who want to argue about whether the statements in mathematics are really true. We will leave these people to argue the problem out with others who know what really true means. Mathematicians, as mathematicians, don't.
Now return to page 14 and pick the right (mathematically speaking) answer.