GMAT考试：Testprep数学精解_GMAT数学

GMAT考试：Testprep数学精解

　　If-Then

　　By now you should be well aware that if the premise of an if-then statement　is true then the conclusion must be true as well. This is the defining characteristic of a conditional statement; it can be illustrated as follows：　

　　Therefore， B

　　This diagram displays the if-then statement AB， the affirmed premise A， and the necessary conclusion B. Such a diagram can be very helpful in showing the logical structure of an argument.

　　Example：

　　If Jane does not study for the GMAT， then she will not score well. Jane， in　fact， did not study for the GMAT; therefore she scored poorly on the test.

　　When symbolizing games， we let a letter stand for an element. When symbolizing arguments， however， we may let a letter stand for an element， a phrase， a clause， or even an entire sentence. The clause Jane does not study for the　GMAT can be symbolized as ~S， and the clause she will not score well can　be symbolized as ~W. Substituting these symbolssintosthe argument yields the following diagram：

　　~S~W

　　Therefore， ~W

　　This diagram shows that the argument has a valid if-then structure. A conditional statement is presented， ~S~W; its premise affirmed， ~S; and then the conclusion that necessarily follows， ~W， is stated.