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题库 / Prep2007E1-DS-146
If the symbol △ represents either addition or multiplication, which operation does it represent?
(1) a △ b = b △ a for all numbers a and b.
(2) a △ ( b – c ) = ( a △ b ) – ( a △ c )for all numbers a, b, and c.
Statement (1) ALONE is sufficient, but statement (2) alone is not sufficient.
Statement (2) ALONE is sufficient, but statement (1) alone is not sufficient.
BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient.
EACH statement ALONE is sufficient.
Statements (1) and (2) TOGETHER are NOT sufficient.
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1）a+b=b+a,a*=b*a,不能确定到底是加还是乘
2）a+(b-c)=a+b-c，（a+b)-(a+c)=b-c，两者不等
a*（b-c)，（a*b)-(a*c)=a*(b-c）,两者相等，
说明这里只能是乘号