I'm thinking of a number.

• if it is not a multiple of 4, then it is between 60 and 69
• if it is a multiple of 3 it is between 50 and 59
• if it is not a multiple of 6 it is between 70 and 79.

What is the number?

Convert each statement to its contrapositive (the contrapositive of "p implies q" is "not q implies not p"; a proposition is equivalent to its contrapositive).  You'll find that x>70 and x<79 and 4 divides x and 3 doesn't divide x.  The only number that meets all of these is 76.

Posted by lmnop on 2004-09-26 16:37:04